Fetal development takes on a new meaning in the second trimester. The characterizing features of the 2nd trimester include finding out the baby’s sex and feeling the baby move.
Find out what happens during The 1st Trimester here.
As the pregnancy progresses, you might hear the heartbeat during a prenatal appointment and your belly will continue to grow. During these changes to your body, fetal development takes on a new meaning. Two months ago, the baby was simply a cluster of cells. Now he or she has functioning organs, nerves and muscles.
The following weekly calendar explains the fetal development during the second trimester with approximate measurements.
Week 13: Intestines move into place and urine is created
During this week the baby’s intestines will move back to his or her abdomen from the umbilical cord. The unbilical cord is where they have been developing during the past couple of weeks. Urine is also forming which is discharged into the amniotic fluid.
Around the baby’s head, arms and legs tissue is developing which will soon become bones, futhermore muscles are growing longer and more structured.
Week 14: Baby’s sex becomes apparent
Week 14 of the pregnancy, or week 12 after conception, the baby’s arms have almost reached the final relative lengths they’ll be at birth, while the lower limbs may be a little shorter, and the baby’s neck has become more defined. The liver and spleen begin to produce red blood cells. The cheekbones are visible and the nose is more noticeable.
The male and female genitalia have formed and the baby’s sex will become apparent this week or in the coming weeks. For girls, ovarian follicles begin forming this week, while the prostate appears in boys.
By now the baby might measure almost 90mm long from crown to rump and weigh about 40 grams.
Week 15: Baby’s skeleton develops bones
Fifteen weeks into the pregnancy, or 13 weeks after conception, the baby is growing rapidly. The skeleton is developing bones, which will become visible on ultrasound images in a few weeks. The large bones that constitute the scalp begin to form and harden, while the scalp hair pattern also is forming. The skin of the baby is covered with a substance that disappears before birth. Moreover, the baby has taste buds and it is able to taste the mother’s food.
Week 16: Baby can make sucking motions
Week 16 of the pregnancy, or 14 weeks after conception, the baby’s eyes have begun to face forward and slowly move towards the centre of the face. The ears are close to reaching their final position. The facial muscles limbs are beginning to function and the baby might be able to make sucking motions with his or her mouth. The baby develops eyebrows and eyelashes and nails are beginning to develop on the fingers and toes.
The baby’s movements are becoming coordinated and can be detected during ultrasound exams, while the heartbeat may now be detected using a stethoscope.
By now the baby might be more than 120mm long from crown to rump.
Week 17: Fat accumulates
Seventeen weeks into the pregnancy, or 15 weeks after conception, toenails have begun to grow. The baby’s urinary tract and circulatory system are functioning and the lungs are inhaling and exhaling amniotic fluid. Moreover, the fetal bones are becoming more visible on the ultrasound and the mother may be able to feel some movement, especially if she has been pregnant before. Soon fat stores begin to develop under the baby’s skin. The fat will provide energy and help keep the baby warm after birth.
Week 18: Baby begins to hear
Eighteen weeks into the pregnancy, or 16 weeks after conception, the baby’s ears are developing the proper shape and begin to stand out on the sides of his or her head. Moreover, the baby might begin to hear. The baby’s eyes may become developed enough to detect light.
If the baby is in a position that reveals the genitals, the ultrasound can discover the sex of the baby since the genitals have formed.
By now the baby might measure 140mm long from crown to rump and weigh 200 grams.
Week 19: Baby’s uterus forms
Nineteen weeks into the pregnancy, or 17 weeks after conception, the white coating called vernix caseosa now covers the entire body of baby. The vernix caseosa helps protect the baby’s delicate skin from abrasions, chapping and hardening that can result from exposure to amniotic fluid. Furthermore, the baby’s arms are developed and the legs reach almost their relative size, which may lead to increased muscle movement and increased sensations of flutters or kicks.
For girls, the uterus, vagina, fallopian tubes as well as the ovaries might begin to form this week. On the other hand, for boys, the male genitalia also forms and becomes recognizable.
By now the baby might measure 153mm long from crown to rump and weigh 240 grams.
Week 20: The halfway point
Halfway into the pregnancy, or 18 weeks after conception, a woman might be able to feel the baby’s movements, also known as quickening. Women who have had previous pregnancies may begin to feel the baby’s movements a few weeks earlier.
The baby’s heart grows stronger, while the sensory cells begin to develop in specialized areas of the brain. Thus, the baby may be able to hear and recognize its mother’s voice. Moreover, immune cells that will protect the baby from viruses are transferred from the mother to the baby at this stage.
By now the baby might measure 160mm long from crown to rump and weigh 300 grams.
Week 21: Baby can swallow
Twenty-one weeks into the pregnancy, or 19 weeks after conception, the baby is poised to gain more weight. At this stage, the baby’s tongue is fully formed and the baby is able to swallow. The white blood cells that form the body’s defence system begin to develop. By this week, the baby is becoming more active and the wake and sleep periods become more consistent.
By now the baby might measure 267mm long from crown to rump and weigh 360 grams.
Week 22: Baby’s hair becomes visible
Twenty-two weeks into the pregnancy, or 20 weeks after conception, the baby is completely covered with a fine, down-like hair called lanugo. The lanugo helps hold the vernix caseosa on the skin. The baby’s eyelids and eyebrows are fully formed and the eyebrows might be visible. Fingernails have grown to the end of the fingers.
Furthermore, with the help of the mother, the baby’s liver may begin to break down bilirubin, which is a substance produced by red blood cells. If the baby is male, the testes begin to descent towards the scrotum and the baby is producing testosterone and forming primitive sperm.
By now the baby might measure 278mm long from crown to rump and weigh 430 grams.
Week 23: Fingerprints and footprints form
Twenty-three weeks into the pregnancy, or 21 weeks after conception, the baby’s proportions are similar to those of a newborn, although thinner because the baby has not developed body fat yet. The skin is wrinkled, more translucent than before and pink to red in color.
This week the baby begins to have rapid eye movements (REM). The baby’s tongue will soon develop taste buds. Fingerprints and footprints are forming, while the bones in the middle ear harden and the baby is able to hear.
With intensive medical care, some babies born this week might be able to survive.
By now the baby might measure 289mm long from crown to rump and weigh 500 grams.
Week 24: Real hair grows
Twenty-four weeks into the pregnancy, or 22 weeks after conception, the baby’s real hair is growing on his or her head. By this week, the baby gains significant weight in organs, muscles and bone mass.
By now the baby might measure 300mm long from crown to rump and weigh 630 grams.
Week 25: Baby responds to voices
Twenty-five weeks into the pregnancy, or 23 weeks after conception, the baby’s hands and startle reflex are developing, improving dexterity. The baby might be able to respond to familiar sounds, such as the mother’s voice, with movement.
Furthermore, the baby’s spinal structures such as the joints, ligaments, and rings begin to develop. The blood vessels of the lungs begin to form and the baby’s nostrils begin to open.
By now the baby might measure 346mm long from crown to rump and weigh 660 grams.
Week 26: Baby’s fingernails develop
Twenty-six weeks into the pregnancy, or 24 weeks after conception, the baby has fully developed fingernails.
The baby’s lungs are beginning make breathing movements and produce surfactant, a substance that allows the air sacs in the lungs to inflate — and keeps them from collapsing and sticking together when they deflate. At this stage, the baby’s eyes are beginning to open or blink and retinas begin to develop.
By now the baby might measure 356mm long from crown to rump and weigh 760 grams.
Week 27: 2nd trimester ends
This week marks the end of the second trimester. At 27 weeks, or 25 weeks after conception, the baby’s lungs and nervous system are continuing to mature, while the brain continues to develop rapidly.
By now the baby might measure 366mm long from crown to rump and weigh 875 grams.
