Japanese Journal of Health and Human Ecology
Online ISSN : 2432-6720
Print ISSN : 2432-6712
ISSN-L : 2432-6712
Original Article
Conception delay and spontaneous and indicated preterm birth among primiparous women in Japan
Shoko KONISHISoyoko SAKATAChiho WATANABEChris Fook Sheng NG
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2018 Volume 84 Issue 4 Pages 117-128


Aim: To examine whether a longer time to pregnancy is associated with preterm births distinguished as either spontaneous or indicated delivery.

Methods: A cross-sectional survey was conducted targeting parous women aged 20-44 years old residing across Japan whose first-born children were singletons. Information on reproductive history including time to pregnancy (TTP) and use of assisted reproductive technology (ART) was collected using internet-based questionnaire. A delivery was judged spontaneous if the mother had either labor and/or membrane rupture at hospital admission. Multinomial logistic regression analyses were performed to estimate odds ratios and 95% confidence intervals (CI) for spontaneous and indicated preterm birth at 34 or at 37 weeks of gestation while adjusting for potential confounders.

Results: The analytic sample was n=4,208 mothers with first-born singletons. After adjusting for age, use of ART, and other possible confounders, women with TTP of 12 months had significantly higher odds of spontaneous preterm birth at 34 weeks (OR 4.55, 95% CI 1.10-18.77) but not at 37 weeks (OR 1.07, 95% CI 0.65-1.75), compared to those with TTP of 6 months. Women with unknown TTP tended to have higher odds of spontaneous preterm birth at 34 weeks (OR 3.67, 95% CI 1.02-13.19) and at 37 weeks (OR 1.38, 95% CI 0.98-1.96), though not statistically significant. There was no significant association with TTP and indicated preterm birth.

Conclusions: Compared to mothers with shorter TTP, those with longer TTP are more likely to experience spontaneous preterm birth.

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© 2018 The Japanese Society of Health and Human Ecology
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