Pregnancy after miscarriage

There is “no need to delay pregnancy after miscarriage,” says BBC News. The website reports that a large study has found that, contrary to current guidelines, conceiving within six months of a miscarriage does not pose a greater risk of the mother having another miscarriage.

How long a couple should wait before trying for another pregnancy after a miscarriage has long been debated, with opinions varying. Current World Health Organization (WHO) guidance recommends that women wait for at least six months before trying to conceive again. This valuable new study examined the medical records of over 30,000 Scottish women and found that conceiving within six months was associated with lower risks of second miscarriage, ectopic pregnancy or termination than conceiving 6–12 months after a miscarriage.

However, the study has several limitations. Most importantly, it cannot tell whether delays between miscarriage and subsequent pregnancies were due to couples choosing to wait before trying again or caused by difficulties in conceiving, which may also be related to problems when pregnancy does occur. Overall, the study suggests that pregnancy can be successful soon after miscarriage, although it is important that prospective parents feel emotionally and physically prepared before trying again.

Where did the story come from?

The study was carried out by researchers from the University of Aberdeen and funded by the Chief Scientist Office in Scotland. It was published in the peer-reviewed British Medical Journal.

The news stories generally reflect the findings of this well-conducted study, but in suggesting that waiting to conceive again is the cause of increased pregnancy complications they have not identified the important considerations that must be made when interpreting the possible reasons behind these findings. The tone of some newspapers might also suggest that the findings of this study constitute new advice on when to conceive again after pregnancy, but it should be noted that there has been no change in the official advice of the World Health Organization, which suggests women should wait at least six months before trying to conceive again.

What kind of research was this?

This was a retrospective cohort study looking at a large population of pregnant women receiving care at Scottish hospitals between 1981 and 2000. The aim was to determine the optimum time interval to leave between miscarriage and trying to conceive again, looking particularly at how this interval was associated with the risk of further miscarriage, ectopic pregnancy, or other pregnancy-related and labour complications.

It is recognised that women who suffer a first miscarriage are at slightly higher risk of miscarrying again, and also possibly of other complications in pregnancy. How long a couple should wait before trying for another pregnancy after a miscarriage has long been debated, with varying opinions between different clinicians. Some believe it is best for women to wait in order to increase the chances of full physical and emotional recovery before trying again, while others believe that a delay will not improve chances of a better outcome and that getting pregnant again fairly soon could help the couple recover more quickly from the loss. The issue is further complicated by the increasing number of women who are having children after the age of 35, as waiting longer at this age can further decrease their chances of conceiving.

Current guidelines from the World Health Organization (WHO) recommend that women should wait for at least six months before trying to conceive again. This study is reportedly one of the first to try to examine the evidence supporting this time interval in the developed world.

What did the research involve?

This research used data from the Scottish morbidity records that collect information on all hospital admissions in Scotland. The records are reported to be 99% complete since the late 1970s and undergo regular quality assurance checks.

The researchers collected data on women who had a miscarriage recorded for their first pregnancy between 1981 and 2000 and who went on to have a second pregnancy. They looked at the dates of the first pregnancy-related records and the second pregnancy records and divided women into groups according to the time interval between miscarriage and next pregnancy: fewer than six months, 6–12 months, 12–18 months, 18–24 months and over 24 months. They excluded women with multiple pregnancies (e.g. twins) and women with an interval of less than four weeks between hospital records, as these visits were presumed to relate to the same pregnancy. In their analyses, they used the current recommended interval of 6–12 months as the reference category against which all the other time intervals were compared.

The main outcomes of interest in the second pregnancy were miscarriage, ectopic pregnancy, termination, stillbirth and live birth. Further outcomes examined included pregnancy and labour complications of pre-eclampsia, placenta praevia (placenta lying over the cervix), placental abruption (placenta detaching from uterus), premature delivery (less than 37 weeks) and very premature delivery (32 weeks or less), and low birthweight infants (less than 2,500g). In their analyses the researchers adjusted for possible confounders of the mother’s age, socioeconomic status, smoking status (known for only 57% of women) and other pregnancy-related factors such as induction of labour.

What were the basic results?

A total of 30,937 women were included in the study. Of them, 41.2% conceived within six months of a miscarriage, 25.2% after 6–12 months, 9.6% after 12–18 months, 6.4% after 18–24 months and 17.6% after 24 months. In general, women with the shortest interval between pregnancies tended to be older (26 on average), be of a higher social class and be less likely to have smoked.

The highest rate of successful second pregnancy was among the women who conceived within six months of their first pregnancy, 85.2% of whom gave birth to a live baby. The lowest rate was among women who conceived again after 24 months, 73.3% of whom gave birth to a live baby. Compared with women who had the standard interval of 6–12 months between pregnancies, women who conceived within six months were:

• 34% less likely to have another miscarriage (odds ratio [OR] 0.66, 95% confidence interval [CI] 0.57 to 0.77)
• 57% less likely to have a termination (OR 0.43, 95% CI 0.33 to 0.57)
• 52% less likely to have an ectopic pregnancy (OR 0.48, 95% 0.34 to 0.69)

Women with more than 24 months between pregnancies were significantly more likely to have an ectopic second pregnancy (OR 1.97, 95% 1.42 to 2.72) or termination (OR 2.40, 95% CI 1.91 to 3.01) than women who conceived within 6–12 months. However, they were not at increased risk of second miscarriage.

Compared to those in the 6–12 months group, women conceiving within 18–24 months were at no increased risk of any adverse outcomes, and women conceiving between 18–24 months were at increased risk of termination only. The risk of stillbirth did not differ between any of the groups.

Compared to the 6–12 months group, women conceiving within six months were less likely to have a caesarean section (OR 0.90, 95% CI 0.83 to 0.98), premature delivery (OR 0.89, 95% CI 0.81 to 0.98) or low birthweight baby (OR 0.84, 95% CI 0.71 to 0.89). However, these were the only significant differences in pregnancy-related complications found between the 6–12 month group and any other group.

How did the researchers interpret the results?

The researchers conclude that women who conceive within six months of an initial miscarriage have the best reproductive outcomes and lowest complication rates in their second pregnancy.

Conclusion

This is a valuable study that appears to be one of the first to examine how the time interval between first miscarriage and conceiving a second pregnancy affects pregnancy outcomes in the developed world. How long a couple should wait before trying for another pregnancy after a miscarriage has always been debated, with varying opinions among clinicians. The WHO currently recommends that women should wait for at least six months before trying to conceive again but many believe that, given the increasing age of first-time mothers in the developed world, delaying pregnancy further could increase the chance of difficulty conceiving or having pregnancy-related complications.

The main findings of this study were that, compared with conceiving between 6–12 months after first miscarriage, conceiving within six months was associated with decreased risk of second miscarriage, ectopic pregnancy or termination. Conceiving after 24 months was associated with increased risk of ectopic pregnancy or termination.

The study is well-conducted and has strengths in its large size (over 30,000 women) and use of highly complete, quality-assured medical records. However, this study was dealing with a complex issue and there are several factors to consider, such as whether or not delays in conceiving were actually deliberate. While the time interval between pregnancies can be accurately assessed from records, this cannot tell us how long the couple actually waited before trying to conceive again.

This is an important issue because while a woman may not have become pregnant again until more than six, 12, 18 or 24 months after her first miscarriage, she may have been trying to conceive again within six months of the first pregnancy. Underlying biological reasons may be behind both difficulty in conceiving and the increased risk of complications when pregnancy did eventually occur. Overall, it is difficult to conclude that waiting, as opposed to having trouble conceiving, is associated with increased risk of complications.

There are a number of other points of discussion, outlined below.

• There may be other differences between the groups of women who conceived at different times after their first miscarriage, which may be affecting the results (called confounding). The researchers adjusted for some factors that could affect results (such as age and socioeconomic status), but there may be other unknown or unmeasured factors having an effect.
• Although the records were quality-assured and 99% complete, they can only provide information on women who actually presented for medical attention with their first and second pregnancies. For example, they may not include details of any women that became pregnant but miscarried within a couple of weeks and did not present to their doctor, either through not knowing they were pregnant or knowing but choosing not to seek medical advice.
• There is some possibility that women were placed into the wrong time interval groups between miscarriage and their next pregnancy. Documentation of first miscarriage in medical records may not be precise as to the time that miscarriage actually occurred; also with the subsequent pregnancy there is the possibility of inaccurate recording of pregnancy duration due to thinking a pregnancy was of fewer or greater weeks’ gestation than it actually was (though current ultrasound technology makes this error less likely).
• It is encouraging that for all women who had previously miscarried, a high proportion had a successful subsequent pregnancy, regardless of how much later the subsequent pregnancy occurred (the lowest rates were in the group who had a greater than 24-month interval between the pregnancies, but almost three quarters still had a successful pregnancy resulting in a live baby).

Despite the limitations of the research, these findings suggest that a successful pregnancy can be achieved within six months of a miscarriage. The decision of when to try and conceive again is fundamentally the choice of the individual couple, and the most important point is that the prospective mother feels physically and emotionally ready to try again. As the researchers of this study have also said, it is important for women who have miscarried to receive support and counselling on how to optimise their own health before and during pregnancy. Part of this guidance should include information on the possible risks and benefits of delaying further pregnancy, which could help prospective parents to make their own informed decision on when to try conceiving again.