More babies often can mean more risks during pregnancy. Women carrying multiples have a higher chance of developing pregnancy-related complications such as preeclampsia, placental problems, gestational diabetes and hypertension than moms carrying singletons. Moms of multiples also have a higher risk of suffering moderate to severe symptoms of postpartum depression than women who give birth to single babies.
When you increase the number of babies you're having, either naturally or with fertility treatments, you increase the odds of complications during your pregnancy -- and you also increase the risk of birth complications.
A woman carrying a single fetus and having a normal pregnancy, for example, can expect her pregnancy to last from 37 to 42 weeks, averaging a 40-week pregnancy. It's estimated that while fewer than two out of 100 singleton pregnancies end before 32 weeks gestation, as many as one out of eight twins and one of three triplets are born less than 32 weeks gestation. With each additional fetus, the length of pregnancy gets shorter, and the average birth weights are also lower. This is important because premature babies may have complications such as respiratory distress, infection and bleeding in the brain because their brain, eyes, lungs, circulatory and intestinal systems are not fully developed at the time of delivery.
On average, a singleton baby is born weighing 7 pounds (3.2 kilograms) while a quadruplet weighs just an average of 3 pounds (1.4 kilograms) at birth. Twins average 5.5 pounds (2.5 kilograms) and triplets average just 4 pounds (1.8 kilograms) each [source: ASRM]. Fewer than 40 percent of babies weighing less than 2 pounds, 3 ounces (0.98 kilograms) at birth survive, and more than 25 percent of those who thrive do so with a disability. Low birth weights put babies at risk for cerebral palsy, for example, which is four times more likely in twins than in singletons, and even greater in triplets or high-order multiples [sources: McKenzie, ASRM].
While the number of twins born in the U.S. continues to increase, triplet and other high-order multiple births are decreasing. This may be due to tighter recommendations in the U.S. (and tighter laws in countries such as England and Canada) regarding the number of embryos transferred per IVF cycle, a number which in the U.S. is based on the patient's age and the quality of the embryos. Currently, the American Society for Reproductive Medicine recommends one to two embryos transferred to women under the age of 35 and up to five in patients ages 40 and older [source: ASRM]. Patients also have a relatively new ART option called elective single-embryo transfer (eSET), an IVF procedure that transfers only a single embryo per cycle and is considered to be as successful as multiple embryo transfers in women ages 35 and younger. This option, clearly, reduces the likelihood of twinning.
If you're looking for an unassisted way of increasing your odds of conceiving twins, consider a visit to Cândido Godói, Brazil, a town where 80 families have 38 pairs of twins -- the locals haven't ruled out the water.