Birth Interval for Pregnancy: The Just Right “Goldilocks Phenomenon”

Achieving a healthy baby following IVF is a joyous occasion and the goal for everyone. Due to laboratory advances and heightened attention focusing on elective single embryo transfers (eSET) of excellent quality Day 5 embryos the very best fertility centers are achieving pregnancy rates greater than 50% for women under 35 years of age and rates over 60% for donor egg recipients. Following transfer many have excellent quality embryos remaining that can be electively frozen (vitrified) for a subsequent frozen embryo transfer or FET cycle, if desired.

The precise timing of recycling to achieve another pregnancy following a successful pregnancy has not been well appreciated. A recent study from Canada published in the American Journal of Obstetrics and Gynecology (2014;210:564, e1-8) and an accompanying editorial addressed the interval between pregnancies and the incidence of congenital anomalies and introduced a “Goldilocks phenomenon” for what the interpregnancy interval should be. An interpregnancy interval less than 6 months is too short because it confers an increased risk for congenital anomalies, preterm birth, and low birth weight, small for gestational age, stillbirth, and early neonatal death. Too long an interval beginning after 24 months also appears to be associated with adverse outcome. Just right seems to be an interpregnancy interval between 18 and 24 months as this interval is associated with the lowest perinatal risk.

Reasons for the association between interpregnancy interval and congenital anomalies and adverse outcome are many but predominately involve maternal depletion of nutrient stores especially when a woman becomes pregnant while or shortly after discontinuing breast feeding. Other factors such as socioeconomic factors, excess or deficient maternal body weight, maternal medical conditions, life style choices and age may also contribute. How to get it just right involves making the right choices. Choose to take prenatal vitamins containing folic acid even when contemplating pregnancy. Choose to maintain a healthy body weight, neither too fat nor too thin. Choose to follow weight gain guidelines during pregnancy. Choose to avoid alcohol, smoking and illicit drugs. Choose to review medications with your health care professional prior to pregnancy. Choose to get vaccinated, keep vaccinations current, and avoid infection. Choose to have all medical conditions optimally managed prior to pregnancy.