Third Trimester: Baby's Developmental Milestones

Featured Article, Reproductive Health, Women's Health
on February 13, 2012

Pregnancy’s third trimester is a busy time for both mother and baby. A mom-to-be hastens to make final preparations for her baby’s arrival, while the baby continues to grow and also prepares to join the world. Most pregnancies are about 40 weeks, but your baby may decide to make his entrance earlier or even a bit later than the due date your doctor has calculated. The baby is active during the third trimester growing, stretching and often kicking Mom with developing little legs.

Weeks 28 and 29. At the start of the first trimester, your baby’s bones are developed but still pliable. His skin is beginning to plump up and smooth out with new fat deposits. The baby can be energetic and may even suffer from hiccups on occasion. According to the Mayo Clinic, babies born premature at week 29 have a “90 percent chance of survival without physical or neurological impairment.”

Weeks 30 and 31. Fetal development milestones at 30 weeks include red blood cells developing in the bone marrow. Your baby’s eyes are staying open more, and she may weigh as much as 3 pounds. By the end of week 31, your baby’s central nervous system is now controlling his body temperature.

Weeks 32 and 33. It’s getting closer to your due date, and the baby has begun to practice breathing, although his lungs are not fully developed. In preparation for life outside the uterus, your baby’s body also has begun to store iron, calcium and phosphorus, reports the University of Maryland Medical Center. His senses are working, including reactions to bright light. The downy lanugo may begin to shed around week 33.

Weeks 34 and 35. You don’t need to schedule your baby’s first manicure, but at 34 weeks, fingernails can reach as long as the fingertips. Weight gain for the baby is rapid, and the vernix caseosa coating begins to thicken as well.

Weeks 36 and 37. Every baby chooses his own time for turning into the head-down position in preparation for birth. Typically, it occurs around week 36. Baby kicks may not feel as strong during the last few weeks before birth, as your baby’s living space is quite crowded due to his rapid growth. Mom will still feel movement, but the sharp kicks of earlier weeks may diminish. Your doctor can tell you how much movement to expect during a normal pregnancy. At the end of week 37, your baby is considered full-term, according to the Mayo Clinic.

Weeks 38, 39 and 40. At week 38, your baby has lost most of the downy lanugo and may weigh as much as 6.5 half pounds. In the last couple of weeks before your baby makes his grand entrance, brain and lung development continues and even the toenails are growing. The baby’s development continues until birth, but don’t worry if he arrives before or even after your calculated due date. Very few babies actually arrive on their scheduled date.