News Release

Study finds variation of the interval between first and second pregnancy

Can influence recurrent spontaneous preterm birth

Peer-Reviewed Publication

Society for Maternal-Fetal Medicine

SAN DIEGO (Feb. 2, 2015)--In a study to be presented on Feb. 5 in an oral concurrent session at 8 a.m. PST, at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting™, in San Diego, researchers will report that the variation of interval from delivery time to conception of the next pregnancy has a strong impact on the risk of preterm birth and low birth weight.

Preterm birth is the most common cause of complications in the newborn in the developed world. The main risk factor for preterm birth is a previous preterm birth. Moreover, both a short and long interval between pregnancies also seems to be of influence on the risk for preterm birth. This study looked at women with preterm birth before 37 weeks of gestation in their first pregnancy and analyzed the association between the intervals of the following pregnancies and the risk for recurrence. The study concluded that an interval of less than 12 months causes an increased risk for severe preterm birth in women who already suffered preterm birth in their first pregnancy. This information should be considered in counseling women with preterm birth in their medical history.

In the study, assessed 11,535 women with preterm birth in the first pregnancy and variations of intervals to the next conception and the impact on the subsequent birth.

The study, titled Can Variation of the Interval Between the First and Second Pregnancy be used as a Therapeutic Strategy to Reduce Recurrent Spontaneous Preterm Birth? Assessed 11,535 women with preterm birth in the first pregnancy and variations of intervals to the next conception along with the impact on the subsequent birth.

"Women with preterm birth are advised to postpone their next pregnancy for at least 12 months to prevent another preterm birth," stated Bouchra Koullali, M.D. who is with the Academic Medical Center obstetrics department in Amsterdam.


A copy of the abstract is available at and below. For interviews please contact Vicki Bendure at 202-374-9259 (cell).

The Society for Maternal-Fetal Medicine (est. 1977) is the premiere membership organization for obstetricians/gynecologists who have additional formal education and training in maternal-fetal medicine. The society is devoted to reducing high-risk pregnancy complications by sharing expertise through continuing education to its 2,000 members on the latest pregnancy assessment and treatment methods. It also serves as an advocate for improving public policy, and expanding research funding and opportunities for maternal-fetal medicine. The group hosts an annual meeting in which groundbreaking new ideas and research in the area of maternal-fetal medicine are shared and discussed. For more information visit


Authors: Bouchra Koullali1, Esme Kamphuis1, Christianne de Groot2, Eva Pajkrt1, Michel Hof1, SarahRobertson3, Ben Willem Mol3, Anita Ravelli1 1Academic medical center, Obstetrics, Amsterdam, Netherlands, 2VU medical centre, Obstetrics, Amsterdam, Netherlands, 3Robinson Research Institute, Adelaide, SA, Australia

Objective: Women who have suffered spontaneous preterm birth (PTB) are at increased risk for repeat PTB. We assessed whether, in women who suffered spontaneous PTB, variation of the time to conception of the next pregnancy would affect the PTB rate.

Study Design: We used a population based longitudinal dataset of the National Perinatal Registry the Netherlands. We linked data of women who had two subsequent singleton pregnancies between 1999-2007 and selected women with spontaneous PTB <37 weeks in the first pregnancy. Women with a pregnancy complicated by congenital abnormalities, stillbirth or primary caesarean section were excluded. We studied the impact of the delivery - time to conception interval on the course of the second pregnancy. Outcomes studied were PTB <37 weeks, <30 weeks and birth weight <2500 grams. Furthermore, we analysed the subgroup of women with PTB <30 weeks.

Results: Among 11,535 women with PTB in the first pregnancy, the 25th, 50th and 75th% for time to conception were at 367, 577 and 852 days respectively. Using an interval of 367-577 days as the reference (PTB 15.7%), the rate of PTB in the lower quartile was 17.4% (RR 1.1; 95%CI 0.99 to 1.3) and in the higher quartiles 16.9% (RR 1.1; 95%CI 0.96 to 1.2) and 22.8% (RR 1.5; 95%CI 1.3 to 1.6) respectively. For delivery <30 weeks, these rates were 1.2% (RR 1.6; 95%CI 0.91 to 2.7), 0.7% (ref), 0.6% (RR 0.76; 95%CI 0.40 to 1.5) and 1.3% (RR 1.8, 95%CI 1.1 to 3.1). Birth weight <2500 grams occurred in 9.8%, 6.7% (ref), 8.4% and 12.6% (all p<0.01). Subgroup analysis of the 726 women who initially delivered <30 weeks indicated PTB rates of 12.8%, 5.4%, 4.9% and 8.1%, and PTB rates <30 weeks of 2.1%, 0.8%, 1.0% and 1.5%.

Conclusion: In women with a previous PTB, variation of interval from delivery to time to conception of the next pregnancy has a strong impact on the risk of PTB and birth weight in the next pregnancy. This information should be used in the counselling of women who suffered PTB.

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