Professor, Department of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora

Dr. Hobbins reports no financial relationships relevant to this field of study.

SYNOPSIS: Authors of a recent study surprisingly have shown that the best chances of avoiding another early pregnancy loss is to become pregnant within six months of a miscarriage.

SOURCE: Sundermann AC, Hartmann KE, Jones SH, et al. Interpregnancy interval after pregnancy loss and risk of repeat miscarriage. Obstet Gynecol 2018;130:1312-1318.

A discussion of the interpregnancy interval (IPI) has been a consistent component of preconception counseling. However, most studies dealing with this subject have been cross-sectional studies focusing on three outcomes: preterm birth (PTB), low birth weight (LBW), and small for gestational age (SGA). However, in these studies, three independent variables (previous normal outcomes, late fetal losses, or miscarriages) all have been lumped together. Authors of a recent study homed in on only one category: risk of recurrent pregnancy loss at less than 20 weeks in those who have had miscarriages in their prior pregnancies.

The study was restricted to 514 newly pregnant patients recruited from eight metropolitan areas in North Carolina and Tennessee whose last pregnancies ended in early pregnancy losses. At their initial interview at less than 12 weeks of gestation, the interval between the date of their miscarriage and their last menstrual period in the current pregnancy was tabulated. Also, the patients were asked how long during their IPIs had they tried to conceive. Patients undergoing treatment for infertility were excluded from the study.

Analysis involved IPIs < 3 months, 3 to 6 months, 6 to 18 months, and > 18 months. The overall miscarriage rate was 15.7%, but when patients were older than 34 years of age it was 20%. More than half (58.9%) had IPIs < 6 months and in only 15%, the IPI exceeded 18 months. Interestingly, the lowest repeat loss rate was when IPI < 3 months (7.3% vs. 22.1% in the 6 to 18 months group; adjusted hazard ratio, 0.33; 95% confidence interval [CI], 0.16-0.71). There were no significant differences between any other groupings, although there was a non-statistically significant trend downward in patients with IPIs > 18 months, resulting in an adjusted hazard risk of 0.53 (95% CI, 0.25-1.12). There was no association between the time the patient waited before attempting to conceive and repeat pregnancy loss < 20 weeks. Those with shorter IPIs had a greater tendency to be white, college-educated patients, and those with longer IPI were more likely to be obese and of lower socioeconomic status.

COMMENTARY

Last year, I wrote a Special Feature devoted to optimizing pregnancy outcomes through preconceptual counseling.¹ My recommendations of postponing pregnancy for greater than 18 months was based on the cross-sectional data from the literature on all comers or in those having had fetal demise in their previous pregnancies. Sundermann et al’s paper certainly challenges that common admonition, specifically in those whose last pregnancy ended in a miscarriage.

Another study in the same issue of Obstetrics and Gynecology correlating IPI with PTB, LBW, and SGA was enlightening.² Class et al showed in a large Swedish population that a short IPI (< 6 months) and long IPI (> 60 months) were associated with a significant increase in all three of the above adverse outcome variables. However, the authors cleverly looked for possible confounding familial factors by using sibling and cousin comparisons. After accounting for familial predispositions, the only significant outcome variable that remained with short IPI (< 6 months) was PTB. However, after 60 months all three variables were increased significantly.

Although the concept of giving the reproductive tract a chance to recover after a late fetal loss or normal pregnancy may seem to be a reasonable suggestion, the data from the miscarriage study point in the opposite direction — that there might be some benefit to attempting conception within six months while the reproductive system is still “primed” for pregnancy. In contrast, the results from both studies in the December 2017 issue of Obstetrics and Gynecology strongly suggest that waiting until more than 60 months has elapsed certainly is not the best strategy.

REFERENCES

1. Hobbins JA. Preparation for the next pregnancy. OB/GYN Clinical Alert 2017;34:5-8.
2. Class QA, Rickert ME, Oberg AS, et al. Within-family analysis of interpregnancy interval and adverse birth outcomes. Obstet Gynecol 2017;130:1304-1311.