When I was practicing as a doctor, I heard this question every morning on "postpartum rounds" (when the doctors visit all the new moms and babies- one of the most fun parts of working on Labor & Delivery!). Many women know they want a second or third baby, so they want to know how long their body needs to recover before the next pregnancy. A popular recommendation is 1 to 1.5 years as a safe "interpregnancy interval," or, the amount of time a women waits after giving birth to get pregnant again. The Green Journal published a short review of new data on interpregnancy interval in May 2015, curated by Dr. Winston Campbell of the University of Connecticut.
The first study analyzed 40,441 mothers, each with three pregnancies. Like many studies before, the study authors compared all the mothers and pregnancies to each other. Doing this, they found that waiting only 0 to 5 months to become pregnant again was associated with higher risk for preterm birth and low birth weight. Waiting a longer time, 60 to 119 months, was associated with a higher risk of preterm birth, small for gestational age, and low birth weight. However, these researchers went a step further and compared each mother's pregnancies to each other. This is an important step because it takes into account (or controls for) the differences between mothers. It allows us to focus on the influence of the length of time between pregnancies and not other factors that are different from one woman to the next (i.e. her other risk factors for preterm birth and low birth weight). When they compared each woman's pregnancies to each other, the increased risks went away- except for the increased risk of small for gestational age for long interpregnancy intervals. What does all this mean? Dr. Campbell explains, it's possible that the increased risks we thought were associated with interpregnancy interval may actually be due to other factors affecting individual mothers.
So, what is the ideal timing for baby #2 or 3 or 4? Another study in Canada examined congenital anomalies for short and long interpregnancy intervals. They found the ideal timing was 12-17 months (about 1 to 1.5 years) between pregnancies.
Finally, one last study looked at how good different types of birth control were at helping women achieve the safest interpregnancy interval (defined in this study as 1.5 years). They found that Long Acting Reversible Contraceptives- LARC (IUDs, the implant, and the shot) were better than oral birth control pills, condoms, and no contraception.
Take Home Message: Planning enough time between pregnancies is important for your health. Speak to your doctor about the best contraceptive methods to help you achieve the right interpregnancy time for your body and your life.