Dr. Curtis Cook is a maternal-fetal medicine specialist. This means that he works exclusively with high-risk pregnancies.
"In a high-risk pregnancy, it’s usually a mother with a pre-existing medical condition like high blood pressure or diabetes, a baby who has a suspected birth defect, whether it be a heart defect or some other kind of spine defect or whatever it would be, or the third category generally is just a high risk obstetrical situation like a multiple gestation, early labor, early water breaking, vaginal bleeding – things of that nature."
Dr. Cook says that multiple pregnancies are becoming more common, in part because of more technological aids to conception. The increase in multiple pregnancies is also due to the fact that many women are having babies later in life, and that makes them more likely to have twins, or other multiples.
Dr. Cook relies to a great extent on ultrasound. In the early stages of pregnancy, he'll look for instance at the membrane that's separating twins. In later stages, he'll look for signs of gender. Ultrasound also makes it possible to examine the placenta for any possible complications.