Interpregnancy Interval and Risk of Adverse Pregnancy Outcomes: A Register-Based Study of 328,577 Pregnancies in Denmark 1994–2010

Non-linear association between interpregnancy interval after vaginal delivery and singleton preterm birth: a retrospective cohort study

BACKGROUND

The association between interpregnancy interval (IPI) after vaginal delivery and preterm birth (PTB) in singleton has not been elucidated. The aim of this study is to investigate the association between interpregnancy interval after vaginal delivery and preterm birth.

METHODS

Birth data from the 2022 National Vital Statistics System (NVSS) were selected, and multinomial logistic regression models were used to determine the odds ratios (OR) and 95% confidence intervals (95% CI) for the association between IPI after vaginal delivery and PTB. A restricted cubic spline (RCS) model with multivariate adjustment was constructed with a 4-node OR curve to check for possible non-linear relationships. Threshold effect analysis was conducted using two-piecewise linear regression and a likelihood ratio test.

RESULTS

The study included a total of 1,517,106 subjects, with an average age of 30.56 ± 5.29 years. 113,613 subjects had PTB, while 1,403,493 did not. Compared to the reference group (18-23 months), IPI of ≤ 11 months and ≥ 24 months were associated with an increased risk of PTB. The RCS curve observed a J-shaped association between the IPI after vaginal delivery and PTB (P < 0.001), with the lowest point of PTB risk occurring at approximately 23 months. The effect values for < 23 months and ≥ 23 months were 0.975 (95% CI: 0.974 ~ 0.977, P < 0.001) and 1.006 (95% CI: 1.005 ~ 1.006, P < 0.001), respectively. The results of sensitivity analyses remained stable.

CONCLUSION

In patients with a history of vaginal delivery, a J-shaped non-linear relationship was found between the IPI and the risk of PTB. IPIs of ≤ 11 months and ≥ 24 months were associated with an increased risk of PTB.

Postpartum hormonal contraceptive use in Denmark during 1997-2021

OBJECTIVE

To provide an overview of postpartum hormonal contraceptive (HC) use in Denmark.

METHODS

This descriptive study used National health registries to estimate the cumulative incidence of HC initiation one year after delivery by type, calendar year, and age group among all first- and second-time mothers who delivered during 1997-2021 in Denmark. Timing of initiation is reported as the median time from delivery.

RESULTS

A total of 676 759 first-time and 552 142 second-time mothers were registered, with a cumulative incidence of HC initiation of 41.0% (95% CI, 40.9-41.1) and 40.5% (40.4-40.6), respectively. From 1997 to 2021, the cumulative incidence of first-time mothers who initially used progestogen-only pills increased from 3.8% (3.5-4.0) to 14.4% (13.9-14.8) and intrauterine levonorgestrel-releasing systems from 0.1% (0.1-0.2) to 12.6% (12.3-13.0). In contrast, combined oral contraception initiation decreased from 31.3% (30.7-31.8) to 7.8% (7.5-8.2). The median time of initiation decreased from 4.7 (Q1-Q3, 2.5-7.5) months during 1997-2001 to 2.5 (2-0-4.0) months during 2017-2021. The cumulative incidence of first-time mothers using combined HC six weeks after delivery decreased from 1.5% (1.5-1.6) during 2007-2011 to 0.5% (0.5-0.5) during 2017-2021.

CONCLUSIONS

Within the first year after childbirth, 41 % of first- and second-time mothers initiated HC in Denmark. Throughout 1997-2021, mothers started earlier after delivery and more often used progestogen-only contraception. Few started combined HC within 6 weeks after delivery. Taken together, the pattern of HC use over time reflects a change to safer contraceptive methods postpartum which minimizes thromboembolic risk.

Short inter-pregnancy interval and birthweight: a reappraisal based on a follow-up study of all women in Norway with two singleton deliveries during 1970-2019

We studied mean changes in birthweight from the first to the second delivery according to length of the inter-pregnancy interval. We also studied recurrence risk of low birthweight, preterm birth and perinatal death. We followed all women in Norway from their first to their second singleton delivery at gestational week 22 or beyond during the years 1970-2019, a total of 654 100 women. Data were obtained from the Medical Birth Registry of Norway. Mean birthweight increased from the first to the second delivery, and the increase was highest in pregnancies conceived < 6 months after the first delivery; adjusted mean birthweight increase 227 g (g) (95% CI; 219-236 g), 90 g higher than in pregnancies conceived 6-11 months after the first delivery (137 g (95% CI; 130-144 g)). After exclusion of women with a first stillbirth, the mean increase in birthweight at inter-pregnancy interval < 6 months was attenuated (152 g, 95% CI; 143-160 g), but remained higher than at longer inter-pregnancy intervals. This finding was particularly prominent in women > 35 years (218 g, 95% CI; 139 -298 g). In women with a first live born infant weighing < 2500 g, mean birthweight increased by around 1000 g to the second delivery, and the increase was most prominent at < 6 months inter-pregnancy interval. We found increased recurrence risk of preterm birth at inter-pregnancy interval < 6 months, but no increased recurrence risk of low birthweight, small for gestational age infant or perinatal death. In conclusion, we found the highest mean increase in birthweight when the inter-pregnancy interval was short. Our results do not generally discourage short pregnancy intervals.

Inter-pregnancy interval and placental weight. A population based follow-up study in Norway

INTRODUCTION

We studied changes in placental weight from the first to the second delivery according to length of the inter-pregnancy interval.

METHODS

We followed all women in Norway from their first to their second successive singleton pregnancy during the years 1999-2019, a total of 271 184 women. We used data from the Medical Birth Registry of Norway and studied changes in placental weight (in grams (g)) according to the length of the inter-pregnancy. Adjustments were made for year and maternal age at first delivery, changes in the prevalence of maternal diseases (hypertension and diabetes), and a new father to the second pregnancy.

RESULTS

Mean placental weight increased from 655 g at the first delivery to 680 g at the second. The adjusted increase in placental weight was highest at inter-pregnancy intervals <6 months; 38.2 g (95 % CI 33.0g-43.4 g) versus 23.2 g (95 % CI 18.8g-27.7 g) at inter-pregnancy interval 6-17 months. At inter-pregnancy intervals ≥18 months, placental weight remained higher than at the first delivery, but was non-different from inter-pregnancy intervals 6-17 months. Also, after additional adjustment for daily smoking and body mass index in sub-samples, we found the highest increase in placental weight at the shortest inter-pregnancy interval. We estimated no difference in gestational age at delivery or placental to birthweight ratio according to inter-pregnancy interval.

DISCUSSION

Placental weight increased from the first to the second pregnancy, and the increase was most pronounced at short inter-pregnancy intervals. The biological causes and implications of such findings remain to be studied.

Effects of Short Interpregnancy Intervals on Adverse Pregnancy Outcomes - Haidian District, Beijing Municipality, China, 2017-2019

What is already known about this topic?

Interpregnancy intervals (IPIs) that are either excessively long or short have been linked with an elevated risk of adverse perinatal outcomes. Presently, no pertinent guidelines have been established in China to provide clear direction with regard to optimal IPI.

What is added by this report?

A brief interpregnancy interval may elevate the risk of miscarriage, postpartum hemorrhage, and fetal distress among expectant women.

What are the implications for public health practice?

These results could inform prenatal consultations, guiding pregnant women towards an ideal interpregnancy interval of no less than 24 months.

Impact of the interpregnancy interval after cesarean delivery on subsequent perinatal risks: a retrospective study

PURPOSE

To assess the impact of the interpregnancy interval (IPI) after cesarean delivery on the risks of adverse perinatal events during subsequent pregnancies.

METHODS

We retrospectively examined perinatal outcomes of subsequent pregnancies of women whose most recent birth experience involved cesarean delivery at our hospital between January 2014 and December 2019. IPI was defined as the time between live birth and subsequent conception. Three IPI groups: < 18 months, 18-60 months, and > 60 months, were assessed. The risks of preterm birth, preeclampsia, placenta previa, placental abruption, fetal growth restriction, and successful vaginal birth were compared among the three IPI groups using uni- and multivariate analyses.

RESULTS

We registered 592 births after cesarean delivery: 178, 288, and 126 in the IPI < 18 months, 18-60 months, and > 60 months groups, respectively. The groups did not differ significantly regarding perinatal outcomes. The multivariate analysis revealed no significant differences in the risks of adverse perinatal outcomes among all groups. The odds ratios (ORs) for preterm birth at < 37 weeks of gestation were 1.24 and 1.64 for those in the < 18 months and > 60 months groups, respectively (P = 0.362 and P = 0.055, respectively). The groups did not differ significantly regarding vaginal birth success rate (ORs 1.72 for the < 18 months group, 0.49 for the > 60 months group; P = 0.486 and P = 0.446, respectively).

CONCLUSION

After cesarean delivery, IPIs shorter than 18 months and longer than 60 months do not significantly impact the risks of adverse perinatal outcomes or successful vaginal birth compared with IPIs of 18-60 months.

Assessing the effects of duration of birth interval on adverse pregnancy outcomes in sub-Saharan Africa: a propensity score-matched analysis

OBJECTIVES

Unlike high-income countries, sub-Saharan African countries have the highest burden of adverse pregnancy outcomes such as abortion, stillbirth, low birth weight and preterm births. The WHO set optimal birth spacing as a key strategy to improve pregnancy outcomes. Estimating the impact of short and long birth intervals on adverse pregnancy outcomes based on an observational study like the Demographic and Health Survey (DHS) is prone to selection bias. Therefore, we used the propensity score-matched (PSM) analysis to estimate the actual impact of short and long birth intervals on adverse pregnancy outcomes.

DESIGN

A community-based cross-sectional study was conducted based on the DHS data.

SETTING

We used the recent DHS data of 36 sub-Saharan African countries.

PARTICIPANTS

A total of 302 580 pregnant women for stillbirth and abortion, 153 431 for birth weight and 115 556 births for preterm births were considered.

PRIMARY OUTCOME MEASURES

To estimate the impact of duration of birth interval (short/long) on adverse pregnancy outcomes, we used PSM analysis with logit model using psmatch2 ate STATA command to find average treatment effect on the population (ATE), treated and untreated. The quality of matching was assessed statistically and graphically. Sensitivity analysis was conducted to test the robustness of the PSM estimates using the Mantel-Haenszel test statistic.

RESULTS

The prevalence of short and long birth intervals in sub-Saharan Africa was 46.85% and 13.61%, respectively. The prevalence rates of abortion, stillbirth, low birth weight, macrosomia, and preterm births were 6.11%, 0.84%, 9.63%, 9.04%, and 4.87%, respectively. In the PSM analysis, the differences in ATE of short birth intervals on abortion, stillbirth, low birth weight, and preterm births were 0.5%, 0.1%, 0.2%, and 0.4%, respectively, and -2.6% for macrosomia. The difference in ATE among the treated group was 1%, 1%, and 1.1% increased risk of abortion, low birth weight, and preterm births, respectively, while there was no difference in risk of stillbirth between the treated and control groups. The ATEs of long birth intervals on abortion, stillbirth, low birth weight, macrosomia and preterm births were 1.3%, 0.4%, 1.0%, 3.4%, and 0.2%, respectively. The ATE on the treated group had 0.9%, 0.4%, 2.4%, 2.8%, and 0.2% increased risk of abortion, stillbirth, low birth weight, macrosomia, and preterm births, respectively. The estimates were insensitive to hidden bias and had a good quality of matching.

CONCLUSION

Short and long birth intervals had a significant positive impact on stillbirth, abortion, low birth weight, macrosomia and preterm births after matching treated and control groups by observed variables. These findings highlighted maternal and newborn healthcare programmes and policies to empower reproductive-aged women to exercise optimal birth spacing to reduce the incidence of stillbirth, abortion, low birth weight, macrosomia and preterm births.

Effect of short inter-pregnancy interval on perinatal outcomes among pregnant women in North-west Ethiopia: A prospective cohort study

Background

Inter-pregnancy interval (IPI) is the elapse of time between the end of one pregnancy and the conception of another pregnancy, while birth to pregnancy interval, is the time gap between live birth and the conception of the next pregnancy. Hence, this study assessed the effects of short inter-pregnancy intervals on perinatal outcomes among women who gave birth in public health institutions of Assosa zone, North-west Ethiopia.

Methods

An institution-based prospective cohort study was conducted among 456 mothers who visited health facilities for the fourth antenatal care appointment (152 exposed and 304 non-exposed). Women who gave their recent birth with the pregnancy interval of <24 months or/and had an abortion history of <6 months were considered as exposed otherwise non-exposed. Data was collected through face-to-face interviews by using questionnaires and checklists. The collected data was entered using Epi-data and exported to STATA for analysis. A log-binomial regression model was used to identify the effect of short inter-pregnancy intervals on the perinatal outcomes.

Results

The overall incidence of adverse perinatal outcomes is 24%. Mothers who had short inter-pregnancy intervals have two times the risk to develop low birth weight (RR: 2.1, 95%CI: 1.16–3.82), and low Apgar score (RR: 2.1, 95%CI: 1.06–2.69). Similarly, the risk to develop small for gestational age (RR: 2.6, 95% CI: 1.19–7.54), and preterm birth (RR: 3.14, 95%CI: 1.05–4.66) was about 3 times among mothers who had short inter-pregnancy interval compared to mothers who had an optimal inter-pregnancy interval.

Conclusion

Short inter-pregnancy interval increases the risk of low birth weight, preterm birth, small for gestational age, and low Apgar score. Health Policy makers, National health managers and health care providers should work on increasing the awareness of optimal inter-pregnancy intervals and postpartum family planning utilization to reduce the effect of short inter-pregnancy intervals on adverse perinatal outcomes.

Interpregnancy interval after a miscarriage and obstetric outcomes in the subsequent pregnancy in a low-income setting, Nigeria: A cohort study

Objectives:

The aim of this study was to determine and compare the occurrence of adverse pregnancy outcomes in a cohort of pregnant women with interpregnancy interval of < and ⩾6 months (short and normal interpregnancy interval, respectively) following a spontaneous miscarriage in their last pregnancies.

Methods:

This was a cohort study that involved pregnant women with a spontaneous pregnancy loss in their last pregnancies. They were recruited at a gestational age of 13–15 weeks and followed up to determine the obstetric and foetal outcomes of their pregnancies at four tertiary hospitals in Nigeria from July 2018 to September 2019. Data collected were analysed using SPSS version 26.0. A Chi-square and multivariate logistic regression analysis were done, and a p-value of less than 0.05 was assumed to be statistically significant.

Results:

A total of 705 participants were studied, out of which 448 (63.5%) and 257 (36.5%) of the participants had short and normal interpregnancy interval after a spontaneous miscarriage. Over 80% of the participants had first-trimester pregnancy losses and were managed with manual vacuum aspiration in 73.3% of the cases. The majority, 87.5% for the normal interpregnancy interval cohort and 86.4% for the short interpregnancy interval cohort, had live births, while 8.5% and 10.1% of the women in the normal and short interpregnancy interval cohorts, respectively, had repeat miscarriages. There was no statistical difference in the occurrence of live births and repeat miscarriages between both cohorts (p > 0.05). There was no increased risk of occurrence of adverse foetomaternal outcomes in both groups (p > 0.05). Multivariate logistic regression analysis showed that there was no statistical difference in the occurrence adverse foetomaternal outcomes between the studied cohorts (p > 0.05).

Conclusion:

There was no significant difference in the occurrence of adverse maternal and foetal outcomes in the cohorts of mothers with short and normal interpregnancy interval following miscarriages in their last previous pregnancies.

Interpregnancy Interval and Subsequent Severe Maternal Morbidity: A 16-Year Population-Based Study From California

Interpregnancy interval (IPI) is associated with adverse perinatal outcomes, but its contribution to severe maternal morbidity (SMM) remains unclear. We examined the association between IPI and SMM, using data linked across sequential pregnancies to women in California during 1997–2012. Adjusting for confounders measured in the index pregnancy (i.e., the first in a pair of consecutive pregnancies), we estimated adjusted risk ratios for SMM related to the subsequent pregnancy. We further conducted within-mother comparisons and analyses stratified by parity and maternal age at the index pregnancy. Compared with an IPI of 18–23 months, an IPI of <6 months had the same risk for SMM in between-mother comparisons (adjusted risk ratio (aRR) = 0.96, 95% confidence interval (CI): 0.91, 1.02) but lower risk in within-mother comparisons (aRR = 0.76, 95% CI: 0.67, 0.86). IPIs of 24–59 months and ≥60 months were associated with increased risk of SMM in both between-mother (aRR = 1.18 (95% CI: 1.13, 1.23) and aRR = 1.76 (95% CI: 1.68, 1.85), respectively) and within-mother (aRR = 1.22 (95% CI: 1.11, 1.34) and aRR = 1.88 (95% CI: 1.66, 2.13), respectively) comparisons. The association between IPI and SMM did not vary substantially by maternal age or parity. In this study, longer IPI was associated with increased risk of SMM, which may be partly attributed to interpregnancy health.

Stillbirth and subsequent pregnancy outcome - a cohort from a large tertiary referral hospital

Objectives This study aimed to assess pregnancy and delivery outcomes in women with a history of stillbirth in a large tertiary referral hospital. Methods This was a retrospective study from Helsinki University Hospital, Finland. The cohort comprised 214 antepartum singleton stillbirths in the period 2003-2015 (case group). Of these, 154 delivered by the end of 2017. Adverse pregnancy outcomes were compared to those in singleton pregnancies of parous women in Finland from the Finnish Medical Birth Register (reference group). Results The rates of adverse pregnancy outcomes were higher among case women for preeclampsia (3.3 vs. 0.9%, P = 0.002), preterm birth (8.5 vs. 3.9%, P = 0.004), small-for-gestational-age (SGA) children (7.8 vs. 2.2%, P < 0.001) and stillbirth (2.7 vs. 0.3%, P < 0.001). There were four preterm recurrent stillbirths. Induction of labor was more common among case women than parous women in the reference group (49.4 vs. 18.3%, P < 0.001). Duration of pregnancy was shorter among case women (38.29 ± 3.20 vs. 39.27 ± 2.52, P < 0.001), and mean birth weight was lower among newborns of the case women (3274 ± 770 vs. 3491 ± 674 g, P < 0.001). Conclusion Although the rates for adverse pregnancy outcomes were higher compared to the parous background population, the overall probability of a favorable outcome was high. The risk of recurrent premature stillbirth in our cohort was higher than that for parous women in general during the study period. No recurrent term stillbirths occurred, however.

Interpregnancy interval and risk of perinatal death: a systematic review and meta-analysis

BACKGROUND

Interpregnancy interval (IPI) <6 months is a potentially modifiable risk factor for adverse perinatal health outcomes.

OBJECTIVE

This systematic review evaluated the international literature on the risk of perinatal death associated with IPI.

SEARCH STRATEGY

Two independent reviewers screened titles and abstracts identified in MEDLINE, EMBASE and Scopus from inception to 4 April 2019 (Prospero Registration #CRD42018092792).

SELECTION CRITERIA

Studies were included if they provided a description of IPI measurement and perinatal death, including stillbirth and neonatal death.

DATA COLLECTION AND ANALYSIS

A narrative review was performed for all included studies. Random effects meta-analysis was used to compare unadjusted odds of perinatal death associated with IPI <6 months and IPI ≥6 months. Analyses were performed by outcome of the preceding pregnancy and study location.

MAIN RESULTS

Of the 624 unique articles identified, 26 met the inclusion criteria. The pooled unadjusted odds ratio of perinatal death for IPI <6 months was 1.34 (95% CI 1.17-1.53) following a previous live birth, 0.85 (95% CI 0.73-0.99) following a previous miscarriage and 1.07 (95% CI 0.84-1.36) following a previous stillbirth compared with IPI ≥6 months. However, few high-income country studies reported an association after adjustment. Fewer studies evaluated the impact of long IPI on perinatal death and what evidence was available showed mixed results.

CONCLUSIONS

Results suggest a possible association between short IPI and risk of perinatal death following a live birth, particularly in low- to middle-income countries.

TWEETABLE ABSTRACT

Short IPI <6 months after a live birth was associated with greater risk of perinatal death than IPI ≥6 months.

The mnemonic code of pregnancy: Comparative analyses of pregnancy success and complication risk in first and second human pregnancies

Obstetrical complications such as spontaneous abortion/miscarriage, fetal growth restriction, preeclampsia or preterm birth occur in approx. 15% of human pregnancies. Clinical experts often state that a previous uncomplicated pregnancy reduces the risk for complications in subsequent pregnancies. Vice versa, a prior pregnancy affected by obstetrical complications increases the risk for reoccurrence. However, published evidence directly underpinning these clinical statements is sparse. Considering that the maternal immune adaptation may be causally involved in determining the outcome of subsequent pregnancies, a comprehensive analysis of clinical data was long overdue. We here present a systematic analysis of clinical data using a PubMed-based approach to identify human studies with relevant information on birth weight and incidences of pregnancy complications in first and second pregnancies. From initially 18,592 publications, 37 studies were included in the quantitative data analysis. Women with a previous pregnancy affected by complications where a derailed immune response can be inferred have a 2.2-3.2-fold increased risk to be affected again in a subsequent pregnancy. Conversely, a normally progressing primary pregnancy reduced the risk for complications in a subsequent pregnancy by 35-65%. Moreover, an uncomplicated primary pregnancy was associated with a 4.2% increased birth weight in a following pregnancy without a difference in gestational age at delivery. In conclusion, the increased birth weight after previously uncomplicated pregnancies suggests that an immune memory is mounted during primary pregnancies. This immune memory may promote the successful outcome of subsequent pregnancies or - if missing or compromised - account for a risk perpetuation of pregnancy complications.

Interpregnancy interval and risk of stillbirth: a population-based case control study

PURPOSE

We examined the association between interpregnancy intervals (IPIs) and stillbirth (defined as fetal death ≥20 weeks), as both short and long IPIs have been associated with adverse perinatal outcomes. Prior pregnancy loss is also a known risk factor for stillbirth, and women who suffer a prior loss often have shorter IPIs. For these reasons, we also sought to quantify the proportion of the association between prior pregnancy loss and subsequent stillbirth risk that may be attributed to a short IPI.

METHODS

We used data from the Stillbirth Collaborative Research Network, a multisite case-control study conducted in 2006-2008, restricted to singleton pregnancies among multiparous or multigravid women (985 controls and 291 cases). We accounted for complex sample design and nonparticipation with weighted multivariable logistic regression.

RESULTS

In the adjusted models, IPIs <6 months, as compared with a reference of 18-23 months, were associated with increased odds of stillbirth (aOR 1.6, 95% CI: 0.8, 3.4). Long IPIs (60-100 months) were also associated with an increased odds of stillbirth (aOR 2.4, 95% CI: 1.2, 4.5). After control for covariates, about one-fifth (21.2%) of the association of prior pregnancy loss (stillbirth, ectopic pregnancy, molar pregnancy, or spontaneous abortion) and stillbirth may be attributable to a short IPI.

CONCLUSIONS

Our results suggest that women who experience a prior pregnancy loss may benefit from additional counseling on adequate birth spacing to reduce subsequent stillbirth risk.

Short interpregnancy intervals and adverse perinatal outcomes in high-resource settings: An updated systematic review

BACKGROUND

This systematic review summarises association between short interpregnancy intervals and adverse perinatal health outcomes in high-resource settings to inform recommendations for healthy birth spacing for the United States.

METHODS

Five databases and a previous systematic review were searched for relevant articles published between 1966 and 1 May 2017. We included studies meeting the following criteria: (a) reporting of perinatal health outcomes after a short interpregnancy interval since last livebirth; (b) conducted within a high-resource setting; and (c) estimates were adjusted for maternal age and at least one socio-economic factor.

RESULTS

Nine good-quality and 18 fair-quality studies were identified. Interpregnancy intervals <6 months were associated with a clinically and statistically significant increased risk of adverse outcomes in studies of preterm birth (eg, aOR ≥ 1.20 in 10 of 14 studies); spontaneous preterm birth (eg, aOR ≥ 1.20 in one of two studies); small-for-gestational age (eg, aOR ≥ 1.20 in 5 of 11 studies); and infant mortality (eg, aOR ≥ 1.20 in four of four studies), while four studies of perinatal death showed no association. Interpregnancy intervals of 6-11 and 12-17 months generally had smaller point estimates and confidence intervals that included the null. Most studies were population-based and few included adjustment for detailed measures of key confounders.

CONCLUSIONS

In high-resource settings, there is some evidence showing interpregnancy intervals <6 months since last livebirth are associated with increased risks for preterm birth, small-for-gestational age and infant death; however, results were inconsistent. Additional research controlling for confounding would further inform recommendations for healthy birth spacing for the United States.

Factors associated with short interpregnancy interval among women treated with in vitro fertilization

PURPOSE

To evaluate factors associated with interpregnancy interval (IPI) among women treated with in vitro fertilization (IVF).

METHODS

Women with at least two cycles of IVF between 2004 and 2013 were identified from the SART CORS database and grouped by age at first cycle, infertility diagnosis, IVF treatment parameters, and cycle 1 outcome (singleton or multiple live birth or no live birth, length of gestation, and birthweight). The distributions of IPIs (in months, 0-5, 6-11, 12-17, 18-23, and ≥ 24) were compared across these factors. IPI was fit as a function of these factors by a general linear model, separately for singleton and multiple live births and no live births at cycle 1.

RESULTS

The study included 93,546 women with two consecutive IVF cycles where the first cycle resulted in a clinical intrauterine pregnancy or a live birth. Among women with a live birth in cycle 1, there was a general pattern of longer IPI for younger women compared to older women. Women with a multiple birth waited longer before initiating a second cycle than women with a singleton birth. For women with no live birth in the first cycle, nearly three fourths initiated cycle 2 within 6 months, regardless of their age. Short (0-5 months) IPI was associated with preterm delivery, older maternal age, and use of donor oocytes.

CONCLUSIONS

Age of the mother, outcome of the first pregnancy, and treatment factors affect the length of the interpregnancy interval. Because short IPI has been associated with poor outcomes, women who are at risk for short IPI should be counseled about these outcome risks.