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Abortions and risks to future babies

“Women who have abortions are more likely to have premature or low birth weight babies in later life”, the Daily Mail said. It reported on a large review which has found that women who have had a previous termination could be at risk of having a subsequent premature birth or a low birthweight baby.

This thorough and well-conducted review combined results from studies looking at terminations over the past 30 years. It found an increased risk of having a premature birth or low birthweight baby if a woman has had a prior termination. This review has some limitations on account of the variable quality and methods of the individual studies it used, and the findings could be explained by several factors including the possibility of changes in medical care and practice since the earlier studies. However, the findings are supported by a body of research and illustrate the importance in giving women all the information so that they can make an informed choice.

The Daily Mail also reports the researchers as being keen the findings are not misinterpreted. It reports Professor Philip Steer, editor in chief of BJOG, as saying, “The most important message is not that this should be used in any way to prevent women having a termination of pregnancy. The effect has to be balanced against the serious effects of forcing women to continue with unwanted pregnancies”.

Where did the story come from?

The research was carried out by PS Shah and colleagues from the Department of Pediatrics at Mount Sinai Hospital and the University of Toronto, Canada. It was funded by Canadian Institute of Health Research. The study was published in the peer-reviewed medical journal British Journal of Obstetrics and Gynaecology.

What kind of scientific study was this?

This research aimed to quantify the risk for women who had previously had a termination and then subsequently had a baby with low birthweight (LBW), a preterm baby (PT) or a baby that was small for gestational age (SGA). Termination is known to be associated with an increased risk of adverse events in future pregnancies, possibly due to infection, cervical damage or scar tissue.

It was a systematic review with meta-analysis, and combined the results of previous studies to investigate the following:

  • Whether the risk of adverse events in later pregnancies is different between women who had ever had a termination with those who had never had one.
  • Assess whether risk increased the more terminations a woman had.
  • To determine whether risk was affected by the method of termination, for example surgical intervention compared to a drug induced termination.

The researchers searched numerous medical databases to identify studies that had examined the associations between terminations and the above outcomes, and compared them to another group of women. Spontaneous abortions (miscarriages) were not included in any of the studies.

All included studies were thoroughly assessed by two reviewers for methods and quality. This included looking for risk of bias in the sample selection, the exposure and outcomes, and adjustments made for possible confounding factors. Any discrepancies were resolved by consensus. Where possible, results were given for studies that had taken into account possible confounders that can also increase the risk of premature birth and low birthweight (for example, age, smoking and so on).

What were the results of the study?

The researchers found 37 studies that were eligible for inclusion.

The meta-analysis of these studies found that having had one previous termination increased a woman’s risk of having a baby of low birthweight by 35% (6.4% compared with 4.9%; odds ratio [OR] 1.35, 95% confidence interval [CI] 1.20 to 1.52), and a premature birth by 36% (8.7% compared with 6.8%; OR 1.36, 95% CI 1.24 to 1.50). However, when they only included studies that had adjusted for possible confounding factors, only the risk increase for prematurity remained significant; the adjusted risk for a low birthweight baby was not increased following one previous termination.

Having more than one termination further increased these risks (72% increased risk of low birthweight baby and 93% increased risk of premature birth). The increases in risk from having had more than one previous termination remained significant even when only studies that had taken into account possible confounding factors were included.

The risk of having a small-for-gestational-age baby was not significantly increased in any analyses.

There were few studies available that provided data on method of termination. Those that did assessed only the surgical methods of vacuum aspiration and dilatation and curettage, and these were not directly compared to each other.

What interpretations did the researchers draw from these results?

The authors conclude that a previous termination is associated with a significantly increased risk of having a premature birth or a low birthweight baby in the future. The risk increases with each additional termination a woman has.

What does the NHS Knowledge Service make of this study?

This is a thorough and well-conducted review, but this type of study has some inherent limitations:

  • It is based on trials from different countries and settings, which used various methods to collect data on terminations (for example, medical records or through self-report by interview). The trials also differed in how they attempted to adjust for confounders (some studies did not adjust for any), and many did not report the method of termination in all cases. Although the authors say that there was only a low to moderate risk of bias, and used a statistical technique when combing the results to take into account their differences, there is still the possibility the risk estimates will not be entirely accurate.
  • There was no reliable indication of which method of termination may carry a higher risk. Only a few of the studies reported their methods (all of which were surgical) and for the majority that did not, it is not clear whether these may have been surgical or medical.
  • There were numerous other factors that may influence risk which the review did not look at (for which relevant information may not have been available in the primary studies). Pregnancy gestation at the time of termination was not considered (for example, under six weeks, six to 12 weeks, or over 12 weeks), and this may have an effect on risk. The reason for termination was also not investigated, and medical complications with a mother or foetus that leads to termination(rather than termination due to unwanted pregnancy), may increase risk in subsequent pregnancies. It was also not known whether or not the women with a history of termination and comparison women had previous pregnancies and children.
  • As the researchers note, the included research spans 30 years and gynaecological and obstetric care and risk may have altered over this time, however minimally.

Whatever the limitations of this review, the results of this and similar studies suggest that there may be an increased risk of having a premature birth or low birthweight baby in subsequent pregnancies following a termination and that the risk may be increased with the more terminations a woman has. The reasons for this are not clearly established, but may include infection as a result of surgical termination or scarring or damage to the cervix that may lead to cervical incompetence.

However, the limitations to the evidence as outlined above must be considered by clinicians who are communicating risk to women, for whom these findings will be of particular relevance. All women considering termination should receive full support and sensitive counselling, and this should include discussion of all possible risks of the procedure, including those related to later pregnancies.

There are a number of different methods of abortion. Which type is recommended for you will depend on how many weeks pregnant you are. The health A-Z article on abortion has more information.

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