Fetal development continues during the third trimester. The baby will open his or her eyes, gain more weight, and prepare for delivery.
The end of the pregnancy is near! Here’s a weekly calendar of events for the third trimester as the due date approaches. Keep in mind that measurements are approximate.
Week 28: Baby’s eyes open
Twenty-eight weeks into the pregnancy, or 26 weeks after conception, the baby’s eyelids are partially open and eyelashes have formed, while the baby’s hair is growing longer. The baby is gaining weight, which is smoothing out many of the wrinkles on his or her skin. Moreover, the baby’s muscle tone is improving and the lungs are capable of breathing.
Babies born during this week that are generally healthy have a 90% chance of survival without physical or neurological impairment; however, the baby’s lungs may require medical attention.
By now the baby might measure 376mm long from crown to rump and weigh 1,000 grams.
Week 29: Baby’s bones are fully developed
Twenty-nine weeks into the pregnancy, or 27 weeks after conception, the baby’s bones are fully developed, but they are still soft and pliable. The baby’s head is in proportion with the body and fat continues to accumulate under the skin. Moreover, the baby may become increasingly sensitive to changes in sound, smell, taste, and sound.
By now the baby might measure 386mm long from crown to rump and weigh 1153 grams.
Week 30: Baby’s eyes are wide open
Thirty weeks into the pregnancy, or 28 weeks after conception, the baby’s eyes are wide open a good part of the time. In addition, the baby may now be able to produce tears. Red blood cells are now forming in your baby’s bone marrow, which transport oxygen and remove waste products such as carbon monoxide. The baby’s toenails are almost fully grown.
By now the baby might measure 399mm long from crown to rump and weigh 1,300 grams.
Week 31: Nervous system development continues
Thirty-one weeks into the pregnancy, or 29 weeks after conception, the baby’s central nervous system has matured to the stage where it can control body temperature. At this stage, the growth rate slows down a little, but the weight continues to increase because fat continues to accumulate under the skin until the rest of the pregnancy.
By now the baby may measure 411mm long from crown to rump and weigh 1500 grams.
Week 32: Baby practices breathing
Thirty-two weeks into the pregnancy, or 30 weeks after conception, the baby’s toenails are formed and visible.
Although your baby’s lungs aren’t fully formed, he or she still practices breathing. The baby’s body begins absorbing vital minerals, such as iron and calcium from the intestinal tract. The layer of soft, downy hair that has covered the baby’s skin for the past few months — known as lanugo — starts to fall off this week.
By now the baby might measure 425mm long from crown to rump and weigh 1700 grams.
Week 33: Baby detects light
Thirty-three weeks into the pregnancy, or 31 weeks after conception, the baby’s pupils can constrict, dilate and detect light entering his or her eyes.
The amniotic fluid is now at its highest during the pregnancy and the baby takes intermittent deep breaths of this fluid. Neurons and synapses are forming connections in the baby’s brain preparing for delivery.
By now the baby might measure 437mm long from crown to rump and weigh 1900 grams.
Week 34: Baby’s fingernails grow
Thirty-four weeks into the pregnancy, or 32 weeks after conception, the baby’s fingernails have reached his or her fingertips. The baby’s eyes are open when awake and closed when sleeping, and the baby has learned to blink. Antibodies from the mother’s blood are further transferred to the baby to continually build immunities until birth.
By now the baby might measure 450mm long from crown to rump and weigh 2100 grams.
Week 35: Rapid weight gain begins
Thirty-five weeks into the pregnancy, or 33 weeks after conception, the baby’s arms and legs are becoming chubby and is gaining weight rapidly. In males, the testes have now fully descended into the scrotum.
Most babies born this week are likely to survive without many long term problems.
By now the baby might measure 462mm long from crown to rump and weigh 2380 grams.
Week 36: Baby takes up most of the amniotic sac
Thirty-six weeks into the pregnancy, or 34 weeks after conception, the crowded conditions inside the mother’s uterus might make it harder for the baby to kick. However, it is likely to experiences lots of stretches, rolls and wiggles. At this stage, the baby’s kidneys are fully developed and the liver begins processing certain waste products. The only organ still left to mature are the lungs.
By now the baby might measure 475mm long from crown to rump and weigh 2620 grams.
Additionally, it is recommended to check on the baby’s movements from time to time (kick count) — especially if the mother notices decreased activity. Ask a health care provider how many movements one should detect in a certain number of hours.
Week 37: Baby is early term
Thirty-seven weeks into the pregnancy, or 35 weeks after conception, the baby will be considered early term. The baby’s organs are ready to function on their own. The baby is still practicing breathing movements and he or she start to develop a grasp with his or her hand.
By now the baby might measure 485mm long from crown to rump and weigh 2850 grams.
To prepare for birth, the baby’s head might start descending into the mother’s pelvis. If the baby isn’t head down, a health care provider will recommend ways to deal with this issue.
Week 38: Baby develops a firm grasp
Thirty-eight weeks into the pregnancy, or 36 weeks after conception, the baby is developing a firm grasp.
The baby has a full head of hair and the toenails have reached the tips of his or her toes. The baby’s brain might weigh about 400 grams. After birth, the baby’s brain will continue to grow. By now the baby has mostly shed all of his or her lanugo.
By now the baby might measure 500mm long from crown to rump and weigh 3080 grams.
Week 39: Placenta provides antibodies
Thirty-nine weeks into the pregnancy, or 37 weeks after conception, the baby’s chest is becoming more prominent. The lungs are maturing and the production of surfactant is increasing.
The placenta continues to supply the baby with antibodies that will help fight infection after birth. Breast milk also provides additional antibodies.
By now the baby might measure 507mm long from crown to rump and weigh 3280 grams.
Week 40: The due date arrives
Forty weeks into the pregnancy, or 38 weeks after conception, the baby might measure 512mm long and weigh on average 3460 grams. However, it is important to remember that healthy babies vary in sizes. The lungs will continue to develop until birth, while there are breast buds present for both sexes by this week.
It is not cause for concern if the due date comes and goes without incident. It is just as normal to deliver a baby a week or two late — or early — as it is to deliver on the actual due date.
