Learn important facts and risk factors for twin pregnancy.

What can you expect when you're having twins? You'll gain more weight, need extra vitamins, and be carefully monitored by your obstetrician. While the rewards of a twin pregnancy are twofold, there are some concerns as well. Learn the basic facts about twin pregnancy.

• There are two types of twins: fraternal and identical. Identical twins are less common than fraternal because identical twins require the splitting of a single fertilized egg, which is very uncommon. Fraternal twins occur when two separate eggs are fertilized by two separate sperm and implant in the womb at the same time.
• The likelihood that you'll have twins is greater if there is a history of twins in your family. Fertility drugs also increase the incidence of twins because they often cause the release of more than one egg during ovulation.
• Your doctor will diagnose a twin pregnancy by listening with a stethoscope to determine if there is more than one heartbeat, or by using ultrasound.
• When you're pregnant with twins, you'll need to eat at least 2,700 calories each day. You'll probably be prescribed extra vitamins and minerals to take. Women pregnant with twins are more susceptible to anemia because more iron is needed to support the healthy growth of two fetuses. Your doctor will also prescribe enough folic acid for the healthy development of your twins.
• With twins, you'll gain between 35 and 45 pounds by the end of your pregnancy. During the first half of pregnancy, your doctor will suggest you gain one pound a week. During the second half, you'll be encouraged to gain a bit more than a pound a week.
• Because of the additional weight, twin pregnancies tend to be more uncomfortable. Get plenty of rest and put your feet up frequently to reduce swelling and leg pain.
• Your doctor will likely monitor your twin pregnancy using techniques such as ultrasound (to check fetal heart rate, levels of amniotic fluid, and fetal growth), cervical exams (to rule out signs of preterm labor), and counting the babies' movements to make sure they are healthy and energetic.
• Twin pregnancies have an increased risk of preterm labor, premature rupture of membranes, uneven growth, high blood pressure, preeclampsia, and diabetes. Your doctor will carefully monitor you for these conditions throughout your pregnancy.
• There is a higher rate of c-section with twins. It's possible to have a vaginal delivery with twins, but it depends on the position and weight of the babies, your health, and the health of the babies.
• Labor is sometimes longer than usual with twins, but the actual delivery is not much longer. Twins are usually born only minutes apart.
• You can certainly breastfeed twins, but you'll need at least 500 additional calories each day to keep up with the demands of producing the necessary breast milk. If you've had twins or are expecting them, be sure to meet with a lactation consultant for special support and advice.