Does medication administered to a woman in labour affect the unborn child?

The following paper was presented by Beverley Lawrence Beech to the Second International Conference of Midwives in Budapest, Hungary, on the 27th October 2004.

Why drugs?

This talk is about drugs given to mothers for pain relief during labour, or for spinal anaesthesia which can also be used for caesarean sections.

Before we start talking about such drugs, we need to ask why such drugs are necessary. Home births, in the UK, which during the last 40 years fell to about 1% of births (even less in some areas) are now increasing, since the government is at last listening to public demand, and research has shown that home birth safe1,2,3,4.

Women who choose to give birth at home, often find they need no pain relief. They are in their own surroundings, they have constant attendance by a midwife, they can eat or drink and change position in labour or give birth as their instincts tell them. Midwives carry gas and air, - with a mask which the mother uses as she feels necessary, and pethidine (a narcotic drug which is injected), but experienced home birth midwives find that this is often effective in smaller doses than those used in hospitals.

Many women hire a birthing pool, and find this very effective for relaxation and relief. How effective it can be can be shown by the dramatic effects on some women who were allowed to use them in hospitals, but ordered to come out of the pool to give birth. The intense and sudden increase in pain actually delayed the birth and was very traumatic. It is interesting that this non-toxic form of pain relief has been strongly opposed by obstetricians, many midwifery managers and bureaucrats - not by openly arguing against it, but by putting every possible obstacle in the way of mothers who wanted it. They have been successful in hospitals - where they controlled the territory - but not in the home, where the mother controlled it. However, it is often made difficult because many midwives insist they are not trained to use this method.

Even outside the home, circumstances affect the need for pain relief. Those mothers who are judged "low risk" and are therefore allowed to use midwifery units, run by midwives, where these exist, use fewer drugs, because they are in a homely atmosphere, and get continuous support from professionals who believe in normal birth. Even in hospital, the many stories we get from mothers confirm that the need for drugs often depends on which midwife is on duty when you are in labour. A number of studies have shown that when women have a doula (a female companion whose job is to support them), they are less likely to need drugs, and less likely to need a forceps or vacuum delivery or a caesarean6. The research powerfully shows that merely going into hospital, away from home, among strangers, being left alone in labour, and sometimes with professionals who are unsympathetic, unable to adopt the most comfortable position, and facing lack of privacy - all these are likely to increase the need for drugs, which affect both mother and child.

However, the greatest need in recent years has been caused by the tendency to induce and speed up labour. Drugs like oxytocin - causing the womb to contract, often with intensity and frequency which Nature did not design us for - and prostaglandins which do the same, but also dilate the cervix - make labour intensely more painful, so that women who have coped well in previous labours, are now unable to do so. Incidentally there seems to be no long-term research on the effect of these drugs on the baby, or possible effects of its experience of birth, but we do know that the development of children is affected by the depression or post traumatic stress disorder in the mother which is a common effect on her of such labours.

Effects of Drugs

There are many ways in which drugs can affect mother, child or the relationship between them - and I am sure we do not know them all. The standard way to measure the condition of a baby after birth is by the Apgar score, used world-wide - which measures colour, tone, breathing and so on. It is a score from 1 to 10 - ten being the top score, at 1 and 5 minutes. But Dr. Virginia Apgar, the American doctor who devised it, had never seen a baby born to an un-medicated mother - so if we scored the behaviour of babies born after normal births at home, what would a REAL top score baby be like? No such standard exists.

Drugs can have so many effects. If they make a mother sleepy they can affect the precious moments of recognition and bonding after the birth If they make the baby sleepy and take away those precious moments of eye contact and recognition, they can also affect bonding - but they can then also affect the baby's ability to latch on to the breast at a time when it is best programmed to learn how to do this. They can depress the baby's respiration, making it vulnerable, and perhaps lead to separation from the mother in a baby care unit.

Thirty years ago our Research Officer, then Chair of the Patients Association, received bitter complaints from mothers who had been drugged for the precious moment of birth, so that they were unaware of it. She discovered that intravenous diazepam - a powerful tranquilliser - was being used, because doctors thought that making the mothers unaware of the birth was a good idea!

This is a useful example of how the doctor's idea of a successful birth was not what mothers wanted. This drug was later dropped when it was found that it adversely affected babies - but it should never have been started. However, good midwives have often told us that drugs are used in hospital to keep mothers quiet, and to make their attendants happier, although the mother would have preferred not to have them.


Effects on the baby's behaviour

Is there any difference between the behaviour of babies who have normal births and those who are exposed to medical interventions and drugs during labour?

In the UK it is common for hospitals to claim that they have a 60, 70, or even 80% normal birth rate; but a study by midwives of births in five maternity units delivering between 1,200 and up to 5,500 women a year revealed that only 1 in 6 first time mothers and 1 in 3 women having second or subsequent labours had what we would define as normal births without drugs or interventions i.e. they did not have their waters broken, no induction or acceleration of labour, no epidural anaesthesia or episiotomy7. It is difficult, therefore, to find babies who have not been exposed to drugs in labour and to judge what the normal behaviour of a newly born baby would be as they are not often seen in large centralized obstetric units.

A small study by researchers in Stockholm, however, videotaped ten babies whose mothers had no drugs during labour. The babies were dried, placed on the mother's chest, covered with a blanket and observed. The babies first massaged their mother's breast for around 11 minutes before they started to feed. Some infants licked or sucked on their hands or fingers around 12 minutes after the birth. The baby then made massage like movements around the nipple, which made the mother's nipple more erect. The infants also licked the nipple. They then began to suck the breast around 80 minutes after the birth. When infants stopped sucking, the hand movements restarted8.

The same team then compared the behaviour of an un-medicated group of babies (Group 1) with a group of 6 mothers who had been given a pudendal block with mepivacaine (Group 2) and a third group of 12 mothers who had a variety of pain relief (Group 3) - in this group eight women had pethidine as well as a pudendal block - though one of these had had an epidural as well, two had had epidurals alone, and two had pethidine alone.

The babies whose mothers had had drugs in labour behaved differently. They cried more after the birth, took much longer to touch the nipple with their hands and to suck.

Hand to mouth movements Hand to nipple movements
Un-medicated babies (Group 1) 12 minutes 25 minutes
Pudendal block (Group 2) 21 minutes Over two hours
Variety of pain relief (Group 3) Over two hours Over two hours
(Ransjo-Arvidson et al., 2001)

Un-medicated babies moved their hand to their mouth around 12 minutes after the birth; pudendal block babies took around 21 minutes. Group 3 babies took more than two hours. Un-medicated babies made their first hand-to-nipple movements around 25 minutes, both of the other groups took more than two hours. First sucking took about 80 minutes in the first group and more than two hours in groups 2 and 3. The proportion of groups who touched their mother's nipple and surrounding area was lower in those whose mothers had had medication, and they were less likely to massage the breast at all. Babies of medicated mothers also had significantly higher temperatures9.

Pethidine and diamorphine

Pethidine is a narcotic drug,. It has become, and remains, the commonest drug injected in labour in the UK , and it is the one such drug which midwives are allowed to carry and use on their own responsibility, without authorisation from a doctor. Yet numerous studies have shown that it is very unsatisfactory as a means of pain relief, and a common side effect is to make mothers vomit - which is very distressing in labour. Diamorphine is a more powerful narcotic, and is more widely used in Scotland. Both can become drugs of addiction.

Drugs used in labour Apgar score less than 7 at 1 minute Apgar score less than 7 at 5 minutes
Diamorphine 12.3% 2.3%
Pethidine 12.3% 1.3%
Entonox 9.1% 1.2%
No drugs 7.5% 1.0%
Chamberlain G et al, 1993

In a large national study of pain relief in labour the National Birthday Trust found that 12.3% of babies exposed to diamorphine in labour had Apgar scores of 7 or less at 1 minute, and 2.3% had Apgar scores of 7 or less at 5 minutes. Entonox had little effect on Apgar scores - 9.1% of babies had an Apgar of 7 or less at 1 minute and 1.2% at 5 minutes. With pethidine low Apgar scores were more common - 12.3% and 1.3%. Of those women who had no drugs in labour 7.5% of babies had an Apgar score of 7 or less at 1 minute and 1% at 5 minutes10.

In 1999 researchers published a study of women in Glasgow who were given pethidine or diamorphine in labour. The study involved 133 women - around half having their first child.

The women who had not given birth before were given 150mg of pethidine and the dose was reduced to 100mg for those having a second or later birth. Those women who were given diamorphine received 7.5mg or 5mg respectively. 17% (28) of the women who delivered within an hour of getting the drugs were excluded from the study. No reasons were given for this unacceptable exclusion.

18% of the women in the pethidine group and 21% of the women in the diamorphine group and went on to have an epidural. At the end of the study 65% of the pethidine group and 57% of the diamorphine group and said their pain relief had been poor or fair.

26% of the pethidine group and 11% of the diamorphine group had an Apgar score of less than 7 at 1 minute.

9 of the pethidine group and 5 of the diamorphine group babies and were admitted to the special care baby unit11

N = 133 Went on to have an epidural Poor to Fair pain relief Apgar Scores less than 7 at 1 minute Babies admitted to Special Care
Pethidine Group 18% 65% 26% 9
Diamorphine Group 21% 57% 11% 5
Note: 28 (17%) of the women were excluded from the study as they gave birth within an hour of the injection.

An intramuscular injtecton of pethidine acts on the mother within 20 minutes and readily crosses the placenta. The baby has greater sensitivity to the drug than an adult, because of the immaturity of the blood-brain barrier and the circulatory bypass of the liver12. Before the birth the mother's liver processes the drug, but if any of the drug remains the baby's immature liver has to take over this processing once the baby is born.

Most midwives try to ensure that pethidine is not given if the baby is expected to be born within an hour, because of the risk that the drug will still be present in the baby's system at birth. However, research shows that pethidine is most likely to cause breathing difficulties if the drug is administered two or three hours before birth. The higher the dose to the mother the greater the effect on the fetus13.

As the baby's liver is immature, it takes a great deal longer for the baby to eliminate the drug from its system (usually 18-23 hours) although 95% of the drug is excreted in 2-3 days. This can have significant implications for breast feeding. Babies suffering the effects of pethidine are often drowsy and unresponsive and researchers have demonstrated that 'Pethidine proved to be the (drug) most inhibiting to breast feeding'. By breast feeding, the mother often unknowlingly, gives the baby a second dose of pethidine as the drug is transferred to the baby through the breast milk14. She may not be aware that pethidine is the cause of her 'sleepy' baby and her problems getting the baby latched on.

Little research has been done into the long-term effects of pethidine on the babies. However, it has been shown that infants with high pethidine exposure were more likely to cry when handled on days 7, 21 and 42, as were those with a high cord blood concentration on day 21. Pethidine also reduced the infant's ability to quiet himself once aroused, and this effect can last for up to six weeks15. The researchers only investigated possible effects on the baby for six weeks and it is interesting that they consider three to six weeks to be 'long-term', when our definition would be in years.

For those babies whose breathing is depressed naloxone is given to reverse pethidine's effects, but the reversal is only temporary unless it is given in an adult dose16. We know of no research which investigates the short or long-term effects of naloxone on the baby.

Epidural anaesthesia

Epidurals are now widely used by maternity hospitals in the UK. This has meant that anaesthetists have to be available round the clock. In one London teaching hospital the epidural rate is over 80 per cent. In fact mothers who want to give birth without epidurals find that midwives are inexperienced at monitoring and supporting those with normal labour. We have had telephone calls from trainee midwives at some hospitals saying that they are near qualifying, but have not yet been able to attend a normal birth - or what hospitals call a normal birth. A few years ago there were complaints to the General Medical Council - the body responsible for medical training - too few normal births were taking place for doctors to practise on, and when one was available, there was intense competition from the midwives.

As a consumer body we should be delighted at the availability of epidurals - indeed in the early days of our history forty years ago, we were campaigning for their availability. However, what has become clear is that this undeniably effective (though not infallible) means of pain relief is used for another purpose. It enables doctors to use high rates of induction and speeding up of labour - which make the birth process into a process Nature did not design women's bodies for. The intense pain which caused a consumer outcry and revolt in the 1970s when induction rates increased, is masked, so women's bodies are used as a production line.

A study that examined the birth records from the Brigham Hospital, Boston, Massachusetts of lower risk women who had had one or two previous caesarean sections from 1994-1995 compared outcomes in babies born to 313 women who had a trial of labour with 136 women who had an elective caesarean.

VBAC Women Baby admitted for Neonatal Care Remained in Neonatal Care for more than 4 hours Mother had signs of fever in labour Baby tested for sepsis Baby given antibiotics
Those who had epidurals (73%) 31.3% 5.2% 16.1% 29.6% 13.9%
Those who did not (27%) 12.1% 1.2% 1.2% 6% 4.8%

What is particularly interesting about this study is the further analysis that was carried out on the VBAC group, comparing outcomes in babies whose mothers had epidurals with those who did not. Nearly three quarters of the women having a VBAC had an epidural (73%). Epidural babies were far more likely to be admitted for neonatal care - 31.3% compared with 12.1% in non-epidural mothers and therefore to have more investigations. They were also more likely to stay there for more than 4 hours - 5.2% compared with 1.2%. Epidurals given in labour tends to cause raised temperatures in mothers, and this often leads doctors to suspect that their babies may have infection at birth. 16.1% of epidural mothers had fevers in labour compared with 1.2% of those who had no epidural. So epidural babies were nearly five times as likely to be evaluated for sepsis (29.6% v 6%) which often involves distressing and invasive procedures like lumbar punctures as well as mother and newborn being separated at a time when they should be bonding, establishing breastfeeding and falling in love with one another. These babies were more than twice as likely to be given antibiotics 13.9% v 4.8%). They were not, however, more likely to have infections since there were only two babies with these, one sepsis, one pneumonia, both in the epidural group17.

So, the increased problems and intervention in the 'trial of labour' babies compared with the elective caesarean babies occurred only in those whose mothers had an epidural.

These are examples of some of the short-term effects of drugs used in labour, but what about long term effects?

Drug addiction in adults

We have constantly criticised the lack of research on longer term effects of drugs in labour. We were then delighted in 1987 to read a paper from the prestigious Karolinska Institute in Stockholm - but what it showed was alarming. Exposure to drugs at birth could cause children to become drug addicts when they grew up. The research did not start by looking at birth, but by looking at increased rates of suicide in young people:

In Stockholm, six senior doctors, led by Dr Bertil Jacobson, at the prestigious Karolinska Institute were intrigued by an increase in suicide rates in young people and the correlation with deaths from cirrhosis of the liver. Could these deaths be affected by some other factor? Their first published paper began by saying

'This paper describes results that we have found both astounding and alarming. ... we believe that the revealed data, irrespective of the underlying mechanism, suggest that obstetric methods should be critically evaluated and possibly modified to prevent damage to future generations'18.

Birth record data were gathered for 412 forensic victims comprising suicides, alcoholics and drug addicts born in Stockholm after 1940, and who died there in 1978-1984. These were compared with 2,901 controls and the researchers looked at the pain-relief policies of the hospitals in which the subjects had been born.

The results were alarming. There was a correlation between birth trauma and later suicide by mechanical means. For example, those who committed suicide by hanging, strangulation or drowning were four times as likely as the controls to have suffered asphyxiation during birth. Mothers of those who died from drug overdoses were twice as likely as controls to have had opiates in labour, and three times as likely to have been given barbiturates.

They then considered cases where opiates or barbiturates were administered within 10 hours of delivery. Of the mothers of the addicts more than twice as many had been administered opiates compared with the controls. Barbiturates were administered about three times as often.

Of particular interest was an accumulation of births of addicts at one particular hospital between 1954 and 1955. During this period, barbiturates were administered routinely to many healthy mothers. Babies born at some hospitals had significantly increased risk of some kinds of death than those born elsewhere.

The following year the researchers published a further paper that looked at whether obstetric medication might affect the risk of the baby becoming an amphetamine addict19.

They examined the birth records of 200 addicts born in Stockholm hospitals and compared them with those of their brothers and sisters. A sample of birth notes on other babies born around the same time was also examined. Information was extracted from case notes by a midwife who did not even know the hypothesis being tested, to avoid possible bias.

The child's risk of becoming a drug addict was related to the place of birth. For example, 14% of the babies were born at one hospital, but it accounted for 27% of the addicts. The hospitals which had used more nitrous oxide produced more addicts. After testing for other variables, the authors found that being born at one hospital increased the risk of later amphetamine addiction 3.7 times.

When addicts were compared with their siblings, their mothers were more likely to have had nitrous oxide for pain relief in labour, and for longer periods. The longer the exposure to nitrous oxide in utero, the greater the risk of later addiction.

In 1990 Jacobson and his colleagues published their investigation into opiate addiction. The birth records of the addicts were compared with those of their siblings. 25% of mothers giving birth to babies who subsequently became opiate addicts had been given opiates (morphine or pethidine) barbiturates, or both, in labour compared with only 16% amongst the control group. And they had been given nitrous oxide for longer; exposure now seemed to be a risk factor for opiate as well as amphetamine addiction. The more drugs given, the higher the risk.

The authors concluded that imprinting at birth could be the mechanism by which some young people are trapped into addiction after trying drugs, whereas others are not. Boys seemed to be more at risk than girls, since testosterone apparently helps imprinting.

They set out to 'test the hypothesis that opiate addiction in adults might stem partly from an imprinting process during birth when certain drugs are given to the mother'20.

One of the criticisms of this research was that it has not been replicated. In Rhode Island, USA, researchers have been following up over 4,000 children born from 1959-66. A previous study of psychiatric problems in these children had identified 69 who developed drug addiction problems. Using the same technique as had already been used in Stockholm, they compared their birth care with that 33 of their brothers and sisters who were also in the long term study. Using siblings as controls means that they would have similar background and social circumstances.

They found that 23% of addicts and only 6% of controls had been exposed to three or more doses of opiates or barbiturates given to the mother within 10 hours of their birth. This means a four to fivefold increase in addiction risk. The researchers checked to see whether other obstetric factors could account for the difference, and they did not.

They conclude

'These findings imply that in utero exposure to high dose medication may be important and preventable risk factor for later substance abuse.'

When we read the first paper, we discussed it everywhere. We asked obstetricians about it at conferences. They turned round and loftily told us the methodology was faulty. We said we had not been able to fault it, and asked how. They were unable to reply. Everywhere we went, doctors were embarrassed, and did not want to talk about it. We have spread the news everywhere, and keep mentioning it. Even in Sweden there were problems. The midwife involved did a doctoral thesis on it. She was refused her Ph.D. on the grounds, as one examiner said "If this is true, it would mean what we have been doing all these years is wrong." There was a scandal in Sweden as a result, a new examining board was set up, and she got the doctorate she was entitled to.

She went on to replicate the research in the United States.

Four years ago, Dr Michel Odent (he who championed water birth) commented on Bertil Jacobson's teams' research stating that the research has never been confirmed or invalidated by further research despite drug addiction being one of the main pre-occupations of our time. In his letter to The Lancet he drew attention to Niko Tinbergen's studies of autistic children which concluded that there are risk factors for autism in the perinatal period, such as anaesthesia during labour and induction of labour21. These comments inspired a study by Ryoko Hattori (1991) who found that 'Kitasato University's method' of delivery is a risk factor for autism. This method is characterized by a combination of sedative, anaesthetic agents, and analgesics, together with a planned delivery induced a week before the due date. That study too has not stimulated further research and Odent speculates that this is because these studies are not 'politically correct'. In other words, doctors are threatened by these findings and are unwilling to explore the issues further, but until they do questions about the adverse effects of drug use in labour on individuals, families and society as a whole will persist.

In 1984 I attended a World Health Organisation conference on drug use in pregnancy and birth in Schlagenbad, Germany. The delegates, from 29 countries, involving cardiologists, consumers, epidemiologists, geneticists, midwives, neonatologists, obstetricians, pharmacologists and toxicologists, concluded that:

'Some obstetric techniques which involve giving drugs have become virtually routine in certain centers or countries; the fact that they are much less widely used elsewhere shows that they are not essential to normal delivery. No form of drug therapy should be used in delivery except where there is a specific indication for it'22.

Whilst medical research is largely drug company funded and governments refuse to fund independent research, the crucial questions about the long-term safety of drug use in labour will never be answered. Large pharmaceutical companies are unwilling to contribute to research they suspect might adversely affect their commercial interests.

So what can be done?

Every pregnant woman should be informed of the risks of drugs in labour. It is interesting how our society is highly critical of women who smoke, drink or take drugs during their pregnancies, but it is totally acceptable to give them far more powerful drugs during their labours without a thought of the possible implications for the baby. Obviously, we cannot suddenly ban pain killing drugs in labour, but we can reduce their use.

In the UK increasing numbers of women are now giving birth at home. In Wales the Government has set a target of 10% of all births taking place in the home by 2007. In areas where home birth has been properly resourced and supported the hospitals have found that their drugs bill has fallen substantially. Women who birth at home rarely use pharmacological drugs. They are not Amazons who will suffer pain no matter what, but because they are in the safety and comfort of their own home they are less anxious, less tense, and more able to cope with the pain of labour. Furthermore, increasing numbers of women choose to use a pool of water for pain relief. Unlike drugs, getting into a pool has no adverse effects and if it is not successful in reducing the pain of labour the woman can get out and then use prescribed drugs.

Research also shows that the continuous presence of a supportive woman has a significant affect on a woman's ability to deal with the pain of labour. Midwives too have been shown to be most effective in reducing the use of drugs and interventions in labour if they are supported to practise midwifery, as opposed to being a handmaiden to the doctor.

We are delighted that you have now set up your own Hungarian Association of Midwives and we wish you well in the work that you will be doing in the future that will undoubtedly do much to improve the health and wellbeing of Hungarian women and babies.

Beverley A Lawrence Beech
Hon Chair


  1. Ackermann-Liebrich U, Voegeli T, Gunter-Witt K et al (1996). Home versus hospital deliveries: follow up study of matched pairs for procedures and outcome, British Medical Journal, Vol 313, pp1313-1318.
  2. Davies J, E Hey, W Reid et al (1996). Prospective regional study of planned home births, British Medical Journal, Vol 313, pp1302-1306.
  3. Northern Regional Perinatal Mortality Survey Coordinating Group (1996). Collaborative survey of perinatal loss in planned and unplanned home births, British Medical Journal, Vol 313, pp1306-1309.
  4. Springer NP and Van Weel C (1996). Home Birth, British Medical Journal, Vol 313, pp1276-1277.
  5. Tew M. Safer Childbirth, Free Association Books, 1998.
  6. Kennell J et al., (1991). Continuous emotional support during labour in a US hospital: a randomised controlled trial. JAMA, 265(17), pp2197-2201.
  7. Downe S, McCormick and Beech BAL (2001). Labour interventions associated with normal birth, British Journal of Midwifery, Vol 9, No 10, pp602-606.
  8. Matthiesen A et al. Postpartum maternal oxytocin release by newborns: effects of infant hand massage and sucking, Birth, 28, pp13-19.
  9. Ransjo-Arvidson et al., (2001). Maternal analgesia, during labor disturbs newborn behaviour: effects on breastfeeding, temperature, and crying, Birth, 28, pp5-12.
  10. Chamberlain G et al. (1993). Pain and its relief in childbirth, Churchill Livingstone.
  11. Fairlie E et al. (1999). Intramuscular opiods for maternal pain relief in labour: a randomized controlled trial comparing pethidine with diamorphine, British Journal of Obstetrics and Gynaecology, 106, pp1181-1187.
  12. Burt RAP, (1971). The fetal and maternal pharmacology of some of the drugs used for pain relief in labour, British Journal of Anaesthesia, 43, pp824-836.
  13. Yerby M, (1996). Managing pain in labour - Part 3: pharmacological methods of pain relief, Modern Midwife, May, p22-25.
  14. Rajan L, (1994). The impact of obstetric procedures and analgesia/anaesthesia during albour and delivery on breastfeeding, Midwifery, Vol 10, No2, pp87-100.
  15. Belsey EM et al., (1981). The influence of maternal analgesia on neonatal behaviour: I. Pethidine. British Journal of Obstetrics and Gynaecology, April, pp398-406.
  16. Weiner PC, Hogg MIJ and Rosen M, (1977). Effects of naloxone on pethidine-induced neonatal depression, British Medical Journal, ii, pp228-231.
  17. Fisler R et al., 2003). Neonatal outcome after trial of labor compared with elective repeat caesarean section, Birth, vol 30, pp83-88.
  18. Jacobson B et al. Perinatal origin of adult self-destructive behavior, Acta psychiatr. scand. 1987: 76, pp364-371
  19. Jacobson B, Nyberg K, Eklund G, Bygdeman M and Rydberg U. Obstetric pain medication and eventual adult amphetamine addiction in offspring. Acta Obstet Gynaecol. Scand. (1988), 67: pp677-682.
  20. Jacobson B et al. Opiate addiction in adult offspring through possible imprinting after obstetric treatment. British Medical Journal, (1990), Vol 301, pp1067-1070.
  21. Odent M. Between circular and cul-de-sac epidemiology, Lancet 15 April 2000, 355, p1371
  22. World Health Oganisation (1984). Thirteenth European Symposium on Clinical Pharmacological Evaluation in Drug Control, Drugs in Pregnancy and Delivery, Schlangenbad, ICP/DSE 105m01, December, 1984.

Further relevant research papers:

  1. Nyberg K et al. Obstetric medication versus residential area as perinatal risk factors for subsequent adult drug addiction in offspring. Paediatric and Perinatal Epidemiology, (1993), 7, pp23-32.
  2. Nyberg K et al. Socio-economic versus obstetric risk factors for drug addiction in offspring. British Journal of Addiction, (1992), 87, pp1669-1676.
  3. Nyberg, K et al. Perinatal medication as a potential risk factor for adult drug abuse in a North American cohort. Epidemiology, 2000, vol 11, pp715-6.
  4. Wiegers TA, Keirse MJN, van der Zee J et al (1996). Outcome of planned home and planned hospital births in low risk pregnancies: prospective study in midwifery practices in the Netherlands, British Medical Journal, Vol 313, pp1309-1313.

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