Table 4: (a) Results from other studies concerning the effect of IPI duration on pregnancy loss after a previous spontaneous or induced termination. (b) Results from studies concerning the effect of IPI duration on pregnancy loss after various previous pregnancy outcomes.
(a)

Study
period/country
SampleEffect of IPIReference category for statistical analysisControlled for

Wong et al. 2015 [6]
USA (EAGeR trial) period 2006–2012
724 pregnant women with 1-2 prior pregnancy lossesNo association between adverse pregnancy outcomes including pregnancy loss and IPI (<3 months or > 3 months)UnknownDemographic and reproductive history characteristics

Makhlouf et al. 2014 [7]
USA, period 2003–2008
Nulliparous women
7681 primigravida
1240 with 1-2 previous spontaneous pregnancy losses (SAB)
817 with a previous induced abortion (IAB)
On fetal/neonatal death and other adverse outcomes after SAB and IAB
No statistically significant difference for various IPI (<6, 6–12, >12 months) on risk of fetal loss and neonatal death
Primigravida
Women with one previous SAB and IPI < 6 months
Maternal age, race, education, smoking, marital status, BMI, and use of vitamins C and E

DaVanzo et al. 2012 [4]
Bangladesh (Matlab), period 1977–2008
9214 women with a miscarriage (spontaneous abortion prior to gestation of 28 weeks)The shorter the IPI following a miscarriage is, the more likely the next pregnancy results in a live birth
No significant effects of IPI duration on risks of a stillbirth Relative risk of a subsequent miscarriage increases with IPI duration
Women with a previous miscarriage and IPI of 6–12 monthsMaternal age, education, gravidity, and calendar year

Love et al. 2010 [5]
Scottish hospital data, period 1981–2000
30,937 women with a miscarriage in first recorded pregnancyOn miscarriage, ectopic pregnancy, IAB, and stillbirth
Women with IPI < 6 months had less likely a miscarriage, highest sign Risk for women with IPI > 24 months
No significant effect of IPI duration on risk of stillbirth
Women with a miscarriage and IPI of 6–12 monthsMaternal age, socioeconomic status, year of first conception, and smoking

Conde-Agudelo et al. 2005 [9]
Latin America period 1985–2002
258,108 women with a previous abortionOn fetal death and other adverse outcomes
No significant difference of effect of IPI on fetal death or on neonatal death
Women with an IPI of 18–23 months Maternal age, parity, education, smoking, marital status, BMI, year of delivery, hypertension, nbr antenatal checks, hospital type, and geographical area

IPI = interpregnancy interval, SAB = spontaneous abortion, IAB = induced abortion, and BMI = Body Mass Index.
(b)

StudySample Effect of IPIReference categoryControlled for

Conde-Agudelo et al. 2006 [3]
Rich and poor countries from all over the world
Meta-analysisOn various adverse perinatal outcomes
Less clear is the association between pregnancy spacing and the risk of fetal (and neonatal) death Curves suggest that IPI < 6 months and IPI > 50 months are associated with increased risks
Differs per included studyVarious factors
Not standard for previous pregnancy outcome

DaVanzo et al. 2007 [11]
Bangladesh (Matlab)
period 1982–2002
66759 pregnancies including multiple births of 28540 womenOn various pregnancy outcomes
An IPI < 6 months after a live birth lead to a 7.5 fold increase for miscarriages, and 1.6 fold increase for stillbirths. An IPI >75 months showed a less increased risk on fetal losses.
After a fetal loss a higher likelihood of a subsequent same fetal loss regardless of the IPI duration
Highest OR on a miscarriage after IPI < 6 months after a life birth
Women with live birth after IPI of 27–50 monthsSocioeconomic status, maternal age, education both spouses, religion, and calendar year

Stephansson et al. 2003 [12]
Sweden, period 1983–1997
410,021 women with two deliveriesStillbirths and early neonatal death
Previous reproductive history and maternal characteristics substantially confounded the association between IPI and risks of stillbirth
Risks are only found for long intervals
Role of short intervals may have been overestimated in previous studies
IPI of 12–35 monthsOutcome of first pregnancy (stillbirth/early neonatal death, preterm delivery, etc.) Maternal age, education, presence of partner, country of origin, diabetes, hypertension, period of delivery, and smoking