The ease of the second trimester recedes as the baby gets bigger and bigger in the third trimester. The mother may experience increased discomfort as the fetus gains weight, stores fat, and gets into position for birth. Pregnancies are considered early term if the baby is born after 37 weeks and full-term at 39 weeks.
At week 28 of pregnancy, the fetus is roughly ten inches long and weighs between two and three pounds. It grows to birth size over the next 12 weeks or so. As the baby takes up more space in the uterus, the mother's breathing often becomes labored because the lungs have less room to expand. Urinary frequency increases due to excess pressure on the bladder. Heartburn, indigestion, and constipation can worsen.
The mother may begin to feel hot because the baby has begun radiating its own body heat. Her ankles, hands, and face may swell slightly and further increases in hormones can make excess hair grow on the arm, legs, and face. The abdominal skin may itch, and stretch marks can appear on the belly, thighs, and breasts. Backaches and leg cramps continue and may increase in intensity. Colostrum, a precursor to breast milk, can leak from the breasts.
Braxton-Hicks contractions are sometimes referred to as practice contractions. While they can happen in the second trimester, they are far more common in the third. During Braxton-Hicks, the uterus tightens for 30 seconds to two minutes. These contractions are not indicative of labor. Women describe them as irregular in intensity and occurrence, non-rhythmic, and unpredictable. Braxton-Hicks do not increase in intensity like labor contractions, and stop and start irregularly.
During the first part of the third trimester, a lot of development is still occurring. The baby's central nervous system stimulates rhythmic breathing movements and can regulate body temperature. Movement increases as the fetus stretches, kicks, and grasps. By the end of week 30, the eyes open completely, red blood cells form in the bone marrow, and the baby may have a full head of hair.
Most major fetal development is complete by week 31. At this point, the baby instead begins putting on weight and preparing for birth. Lanugo, the downy hair that protects fetal skin, begins to fall off. The pupils begin responding to light and the bones start to harden, though the skull remains soft an flexible for passage through the birth canal. By the end of this period, the fetus is about 12 inches long from crown to rump and weighs between four and five pounds.
At week 35, the baby's skin is smooth and pink, and body fat has started to deposit in the limbs. The fetus is so large at this point that the mother may no longer feel punches and kicks because the baby doesn't have enough space to stretch out. That said, rolls and wiggles should still be evident. The baby may flip at this time, getting into the head-down position to prepare for birth.
Breech presentation occurs when the fetus does not naturally move into delivery position. There are a few types of breech. Frank breech occurs when the baby's buttocks are near the birth canal with the feet by the head. Footling breech is when the feet are facing the birth canal rather than the head. Complete breech is when the buttocks are toward the birth canal with the legs bent and feet near the buttocks. Doctors diagnose breech with a physical exam and ultrasound.
One method used to correct breech presentation is external version. The mother receives medication to relax the uterus. Then, the doctor gently pushes on the lower abdomen to attempt to place the closely monitored baby in a head-down position. This technique is generally successful but difficult to do close to the due date. Some natural methods may work, too, including placing headphones on the bottom of the abdomen to encourage the baby to move toward the sound.
For the beginning of the third trimester, prenatal visits continue as they did in the second. Doctors check the mother's blood pressure, weight, and urine, as well as the fetal heartbeat and height of the fundus or top of the uterus. Appointments change from monthly visits to every two weeks and may increase to every week as the due date approaches. Starting around week 38, the doctor will begin cervical checks to assess dilation and effacement.
Signs that labor is imminent include the baby moving into the pelvis, indicating its readiness for birth. This can occur weeks or hours before labor. Vaginal discharge increases and may be slightly bloody. Signs that labor has begun include strong and regular contractions lasting between 30 seconds and a minute, spaced five to ten minutes apart. These contractions are usually strong enough to prevent the mother from walking or talking during them. The water breaks when the amniotic sac ruptures and the amniotic fluid leaks out in a slow trickle or sudden gush.
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