How a Baby Grows in the Second Trimesterby Elizabeth MacDonald
You are growing a baby. This little being is moving inside of you, kicking and twisting, quickly growing and developing into the newborn that you will so lovingly dote over in a few short months.
Welcome to weeks 13-27, better known as the second trimester. Things will seem so much more real once you start feeling your baby, and by the end of this trimester, you may just wonder how much bigger your uterus can get – and you will definitely be feeling some feet near your ribs.
What is happening inside that womb right now? What started as a cluster of cells has continued multiplying and grown into a fetus. There are functioning organs, nerves, and muscles now. The heartbeat can be heard easily with a doppler at your appointments. Remember that every pregnancy and baby is different, so your baby may develop a bit quicker or slower than this timeline. Trust in your ability to grow and nurture this baby while he is inside of you.
The placenta and umbilical cord are now providing oxygen and nutrients for your baby. Even so, she is practicing breathing movements. The amniotic fluid is being used by Baby to ‘breath’ in and out. Her heart is still beating quite fast, and may slow a bit throughout the rest of the pregnancy. Tissue that will become bone is developing in the head and throughout the arms and legs. Her ears and eyes are still developing and will continue to move forward on the head into their permanent places. The skin is covered in a fine hair called lanugo. Her neck is lengthening. Hands and fingers are becoming functional, meaning she can suck her thumb.
Week 14Not only is baby ‘breathing’ amniotic fluid, but he is now ‘drinking’ it as well. This is how the muscles learn to work once introduced to the world, they practice with the amniotic fluid. She can urinate. Yes, your baby can now pee. The intestines have returned to her abdomen from the umbilical cord, where they have been growing for the past couple of weeks. Urine can form and be dispensed back into the amniotic fluid. Baby may be able to hear you. His middle ear bones are hardening. Red blood cells are forming in the spleen. Your baby's sex will become apparent this week (or in the coming weeks). For girls, ovarian follicles begin forming. For boys, the prostate appears. He is now about 3.5 inches long.
Week 15Your baby’s scalp and hair pattern are forming. The bones of the skeleton are continuing to develop. His legs are longer than his arms, and he is now large enough for you to possibly start feeling him use them! The skin is still very thin, but the fingernails and toenails are growing.
An ultrasound would show you just how intense your baby’s movements are right now! She is flipping and marching all over in there! Her eyes are now facing forward. Fat is beginning to form under the skin, and the neck is strengthening. She is sucking, swallowing, and blinking throughout the days now. Baby is measuring around 4.5 inches.
The umbilical cord thickens and there is accumulation in the bowels. Tissue continues hardening to bone. Baby hiccups may be keeping the mother entertained. Fat continues accumulating, helping to regulate baby’s body temperature after birth. Baby is now just over 5 inches long.
Vernix begins to form over the skin and the placenta continues to grow. The lungs and vocal cords develop alveoli. The gender is more accurately predicted by ultrasound at this point or afterward. Your baby may start to react to sounds or voices outside the womb. Growing over ½ an inch this week, he is now over 5.5 inches in length.
Week 19A baby girl’s uterus and vagina are forming. Her permanent teeth are forming behind the baby teeth that are already under the gums. She begins sleeping on the same (or similar) schedule she will follow as a newborn. She now measures just over 6 inches in length.
Week 20The half-way point! 80-90% of babies reveal their gender through ultrasound this week. The uterus is continually expanding to accommodate your baby. Her growth begins to slow down this week and level out to an even growth rate for the remainder of pregnancy. Her nerve cells are developing to experience new senses. She measures about 6.5 inches in length from crown to rump, but measurements are now taken from crown to heel, so she’ll average about 10 inches in length.
Week 21Your baby’s white blood cells form. His skin is opaque, and he is swallowing easily. His tongue is developing.
Week 22The fine hair (Lanugo) is now fully covering your baby. (This helps keeps the vernix on her.) Her eyelids and eyebrows are complete. A boy baby is forming sperm and testosterone, with the testes moving into place. Your baby may be close to weighing a pound now.
Week 23Your baby’s body proportions are almost normal now. His eyes are fully formed, but they do not have color yet. His skin is wrinkled and fingerprints are forming. A girl’s ovaries now hold a lifetime supply of eggs. If he is born now, he will have a 15% chance of survival. This percentage increases each day he is in the womb.
Week 24Your baby’s real hair is growing. The taste buds and lungs are continuing to develop. She is now officially viable, meaning she has a chance at surviving outside the womb with medical help now. Rapid Eye Movement (REM) occurs during her sleep cycles. She is about 11 inches long.
The position and frequent movements of your baby place pressure on the mother’s bladder and make for unpleasant sleep positions. Your baby’s spine is still forming and his nostrils are now opening. He can wiggle his fingers and toes. He is just over 13.5 inches long and close to a pound and a half in weight.
Week 26Your baby's lungs are beginning to produce surfactant, the substance that allows the air sacs in the lungs to inflate. Her finger and toenails are complete. Her retinas are formed and she can open her eyes and blink. There are detectable brain waves in response to hearing and sight. She’s about 14 inches long.
The last week of the second trimester, your baby's lungs and nervous system are continuing to mature. Your baby is about 14.5 inches in length and weighs nearly 2 pounds now.