There are different reasons that a multiple birth occurs. It could be that multiple eggs were released at one time. This results in fraternal twins (or triplets, quadruplets, etc.), who are no more genetically similar than singleton siblings. Assisted reproduction techniques that put more than one fertilized egg into the uterus, such as in vitro fertilization and embryo transfer, may also result in a multiple pregnancy, typically also resulting in fraternal twins. Twins can also result from a single fertilized egg splitting into two – this results in genetically identical twins.
Identical twin births occur worldwide at a constant rate of 3.5 per 1000 births. Fraternal twin (and higher order) pregnancies have become more and more common, mainly due to increased maternal age and the use of assisted reproduction techniques. In 1991, 2.1 % of all births were multiple births. By 2011, this number had risen to 3.3%.
You might feel overwhelmed and excited at the same time to be expecting more than one baby! You may wonder how you will cope. You will need special health care and support while you are pregnant, and after the babies are born. Since women with a multiple pregnancy are at higher risk of some pregnancy complications, most women are cared for by obstetricians. However early pregnancy care may happen with family physicians, nurse practitioners or midwives, and occasionally these care providers will share care with obstetricians or have primary responsibility for care. Specialized care is required because there are some complications of pregnancy that are more common in multiple pregnancies, such as preterm birth and low birth weight. Pre-eclampsia, gestational diabetes, and severe nausea and vomiting are also more common in women pregnant with multiples. Depending on whether the babies each have their own amniotic sac to grow in, or are sharing one, there may be other problems to consider. Obstetricians have expertise in managing and reducing these risks.
Nutrition recommendations are slightly different for mothers of multiples. While the general recommendations stay the same (eat a varied diet, follow Canada’s Food Guide to Healthy Eating, take a prenatal vitamin containing folic acid), you will need to eat a little more to support the growth of multiple fetuses. You will need to consume an additional 200 calories per day in the first trimester, 400 calories (2 servings) per day in the second trimester, and 600 calories (3 servings) per day in the third trimester. These numbers may be even higher for women with higher order multiples.