Low birth weight. While the average single baby weighs 7 pounds at birth, the average twin weighs 5.5 pounds. Triplets typically weigh 4 pounds each, and quads weigh 3 pounds each. Babies born at under 5.5 pounds are considered to have a low birth weight.

Twins are probably still going to be developing in the womb a while longer, but the parents of triplets and other higher-order multiples may be getting close to the end of their pregnancy journeys now!

A little more than half of twin pregnancies end in preterm delivery (before 37 weeks). While 40 weeks is the full gestation period of the average pregnancy, most twin pregnancies are delivered at approximately 36 weeks (range 32-38 weeks depending on the type of twin pregnancy).

The safest, most ideal time for women to give birth to dichorionic twins in otherwise uncomplicated pregnancies is at 37 weeks, found a new study. Women carrying monochorionic twins, appear to have the best outcomes for their newborns when giving birth at 36 weeks, the same study found.

They weigh about 4.2 pounds and measure about 17.2 inches—and may grow up to a full inch this week.

Most babies generally settle in the head-down position around the 33- to 36-week range. This is the ideal and safest position for delivery.

How quickly should I gain weight? Women carrying twins will only gain 4 to 6 pounds during the first trimester and 1 ½ pound per week during the second and third trimesters. If you are carrying triplets, you should expect to gain 1 ½ pound per week throughout the entire pregnancy.

According to the March of Dimes, close to 60 percent of all twins and more than 90 percent of triplets are born prematurely (before 37 weeks). The average twin pregnancy lasts 35 weeks. Triplet pregnancies average 33 weeks, and quad pregnancies average 29 weeks.

The only way you can tell you are having twins is through ultrasound. Baby Centre says the earliest detection can happen around 10 weeks to 13 weeks and six days during a dating scan.

Pre-term (or early) labor resulting in premature births. A typical, single pregnancy lasts about 40 weeks, but a twin pregnancy often lasts between 35 to 37 weeks.

While not all births at 33 weeks can be avoided, some can. Follow your health care provider’s advice for your situation. Stay hydrated and get the rest your body needs. Pay close attention to your body in your final weeks of pregnancy.