Women May Not Need to Delay Pregnancy After an Initial Miscarriage

Laurie Barclay, MD

August 11, 2010

August 11, 2010 — Women may not need to delay pregnancy after an initial miscarriage, according to the results of a retrospective, Scottish population–based cohort study reported Online First August 5 in the BMJ.

"How long a couple should wait before trying for another pregnancy after a miscarriage is controversial," write Eleanor R. Love, from the University of Aberdeen in Aberdeen, Scotland, and colleagues. "Some clinicians believe that there is little justification for delaying the next pregnancy, as an increased interpregnancy interval is unlikely to improve perinatal outcomes, whereas a new viable pregnancy and the birth of a child could enhance the women's chances of recovery.... Current guidelines from the World Health Organization recommend that women should wait for at least six months before trying again, whereas others suggest a delay of up to 18 months, based on reports that interpregnancy intervals of 18-23 months after a live birth can enhance maternal and perinatal outcomes in the next pregnancy."

The goal of this study was to evaluate the optimal interval to subsequent pregnancy after miscarriage in a first recorded pregnancy. At Scottish hospitals between 1981 and 2000, a total of 30,937 women who had a miscarriage in their first recorded pregnancy and subsequently became pregnant were followed up during the second pregnancy. The main study outcome was miscarriage, live birth, termination, stillbirth, or ectopic pregnancy in the second pregnancy, and secondary endpoints were rates of cesarean and preterm delivery, low birth weight infants, preeclampsia, placenta previa, placental abruption, and induced labor in the second pregnancy.

Compared with an interval of 6 to 12 months between the miscarriage and second conception, an interval less than 6 months was associated with lower risks for repeated miscarriage (adjusted odds ratio [OR], 0.66; 95% confidence interval [CI], 0.57 - 0.77), termination (OR, 0.43; 95% CI, 0.33 - 0.57), and ectopic pregnancy (OR, 0.48; 95% CI, 0.34 - 0.69). The risk for an ectopic second pregnancy was greater with an interpregnancy interval exceeding 24 months (OR, 1.97; 95% CI, 1.42 - 2.72), as was the risk for termination (OR, 2.40; 95% CI, 1.91 - 3.01).

Compared with women who had an interpregnancy interval of 6 to 12 months, those who conceived again within 6 months and had a live birth in the second pregnancy were less likely to have a cesarean delivery (OR, 0.90; 95% CI, 0.83 - 0.98), preterm delivery (OR, 0.89; 95% CI, 0.81 - 0.98), or low-birth-weight infant (OR, 0.84; 95% CI, 0.71 - 0.89). However, they were more likely to have labor induced (OR, 1.08; 95% CI, 1.02 - 1.23).

"Women who conceive within six months of an initial miscarriage have the best reproductive outcomes and lowest complication rates in a subsequent pregnancy," the study authors write.

Limitations of this study include potential lack of uniformity in documenting gestational age and outcomes of interest as well as possible misclassification. This study also evaluated only miscarriages that led to hospital contact, and the findings therefore cannot be generalized to all women with a miscarriage.

"Our research shows that it is unnecessary for women to delay conception after a miscarriage," the study authors conclude. "As such the current WHO [World Health Organization] guidelines may need to be reconsidered. In accordance with our results, women wanting to become pregnant soon after a miscarriage should not be discouraged."

In an accompanying editorial, Julia Shelley, associate professor of health and social development at Deakin University in Melbourne, Australia, discusses some of the methodologic issues regarding this study and earlier studies.

"[A]ll of the studies have selection and measurement biases that cast doubt on the value and generalisability of their findings," Dr. Shelley writes. "Of greatest concern is that women with short interpregnancy intervals are more fertile than those whose subsequent pregnancy occurs later because these women seem to have better pregnancy outcomes and fewer complications. Further research into this question may need to wait for data from more sophisticated linked primary care and hospital datasets or specifically designed research studies that can measure and account for such differences, even if they will not be able to control for them."

This research was partially funded by the Chief Scientist's Office in Scotland. Two of the study authors were employed by the University of Aberdeen at the time of doing this research and are independent from the funders. Ms. Love is a medical student, and another study author is employed by NHS Grampian. Dr. Shelley has disclosed no relevant financial relationships.

BMJ. 2010;341:c3967. Abstract

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