Does the time interval between pregnancies have an effect on the next pregnancy?

This study investigated if the interpregnancy interval (IPI; the time between pregnancies) has an effect on the following pregnancy. They found that an IPI of less than 12 months or greater than 60 months is associated with worse pregnancy outcomes.

The interpregnancy interval (IPI) is the time between the end of one pregnancy and the start of another. It is recommended that women wait at least 2 years before becoming pregnant again. For older women, this may not be feasible.

There is evidence to suggest that IPI less than 2 years can have negative outcomes for the pregnancy. The negative outcomes include preterm birth (PTB), low birth weight (LBW) and non-live birth (NLB). Many older women attempt to become pregnant using assisted reproductive techniques (ARTs). In vitro fertilization (IVF) is an ART. It is unclear if IPI is associated with negative outcomes in patients undergoing IVF.

This study included 12,633 IVF deliveries and 1,213,085 non-IVF deliveries. Patient records were obtained to identify the IPI and outcomes of pregnancy. The authors analyzed the risks associated with IPI by comparing this to the outcomes. PTB, LBW, and small gestational age (SGA; newborns who are smaller in size than normal for the time of the pregnancy) were the outcomes analyzed.

The risk of PTB for an IPI between 12 and 24 months was 22.2% for IVF and 6.4% for non-IVF deliveries. For an IPI of less than 12 months, the risk of PTB was 24% higher for IVF and 19% for non-IVF deliveries than a larger IPI. For an IPI of greater than 60 months, the risk of PTB was 12% higher for IVF and 19% for non-IVF deliveries. The risk of LBW and SGA was also higher with IPI of less than 12 months or greater than 60 months. 

The authors concluded that an IPI of less than 12 months or greater than 60 months is associated with worse pregnancy outcomes in both IVF and non-IVF pregnancies.

This study did not include specific information on previous or subsequent pregnancies. This is important as a number of factors might influence these outcomes.