Second Trimester - Fetal Development




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Week 15:  During this week of your pregnancy, which is approximately 13 weeks after conception, the bones of the baby’s skeleton are starting to develop.  Your baby is growing rapidly, and the developing skeleton should soon become visible on the ultrasound images.  At this stage of the pregnancy, the scalp hair pattern on the baby is starting to form.

Week 16:  During this week of your pregnancy, which is approximately 14 weeks after conception, the eyes of the baby have started to face forward and are slowly beginning to move.  The ears are also moving toward what will be their final position, and facial expressions are possible.  The facial muscles are starting to become more developed, and expressions such as frowning and squinting can be noted.  Your baby may also be able to make sucking motions with his or her mouth at this stage of the pregnancy. 
The movements of the baby are becoming more coordinated and may be able to be seen during the ultrasounds, however, they may be too slight at this point to be actively felt by the mother.  Your baby may be more than 4 1/2 inches (120 millimeters) long from crown to rump and weigh nearly 4 ounces (110 grams) at this stage of the pregnancy.

Week 17:  During this week of your pregnancy, which is approximately 15 weeks after conception, the primary developmental feature is the production of fat stores that are beginning to develop under the baby’s skin.  This fat is necessary for the provision of energy, and will serve to warm the baby after it has been delivered.

Week 18:  During this week of your pregnancy, which is approximately 16 weeks after conception, the final position of the ears on either side of the head are noticeable.  The initial stages of hearing are developing for the baby, as the nerve endings between the ears and the brain are becoming established.  At this stage of the pregnancy, your baby may be able to hear the sounds of your bodily functions, such as your heartbeat, the rumbling in your stomach, or the sound of the blood flowing through the umbilical cord.  It may also be possible that these new sounds are startling to the baby!  Your baby may be more than 5 1/2 inches (140 millimeters) long from crown to rump and weigh 7 ounces (200 grams) at this stage of the pregnancy.

Week 19:  During this week of your pregnancy, which is approximately 17 weeks after conception, the baby’s hearing is continuing to improve.  It is possible that the baby may start to hear conversational voices outside of the womb, however, it is likely that the surrounding bodily noises and the natural protective paste that has developed over the baby’s ears will limit the clarity of what is heard!  For girls during Week 19, the formation of the vagina and uterus may have started.

Week 20:  During this week of your pregnancy, which is approximately 18 weeks after conception, you have officially reached the halfway point!   The delicate skin of the baby is covered with coating of vernix caseosa, which often resembles a greasy, cheese-like substance.  At this stage of the pregnancy, the mother may begin to feel the first movements of the baby, which is commonly referred to as the “quickening.”  Your baby may be more than 6 1/3 inches (160 millimeters) long from crown to rump and weigh more than 11 ounces (320 grams) at this stage of the pregnancy.

Week 21:  During this week of your pregnancy, which is approximately 19 weeks after conception, the primary developmental feature is the gaining of more weight by the baby.  The physical activity levels of the baby are increasing, and the baby has started to swallow.

Week 22:  During this week of your pregnancy, which is approximately 20 weeks after conception, the entire body of the baby is covered by lanugo, which is a fine, down-like coating of hair.  The purpose of the lanugo is to help the layer of vernix caseosa adhere to the skin.  It may be possible to see the baby’s eyebrows on ultrasound images.  Your baby may be more than 7 1/2 inches (190 millimeters) long from crown to rump and weigh 1 pound (460 grams) at this stage of the pregnancy.

Week 23:  During this week of your pregnancy, which is approximately 21 weeks after conception, the skin of the baby is more translucent than before, far more wrinkled, and appears to be either red or pink in color.  The movements of the eyes are becoming more rapid, and taste buds are starting to develop on the tongue.  The baby is also starting to form footprints and fingerprints at this stage of the pregnancy.   For girls, the ovaries and uterus are developed and in place, complete with an egg supply that will last a lifetime.  For boys, the testes have developed, and they are beginning to start their descent from the abdomen. 

Week 24:  During this week of your pregnancy, which is approximately 22 weeks after conception, the baby is starting to develop a regular cycle of waking and sleeping.  The presence of a real hair is becoming noticeable on the head.  Your baby may be more than 8 inches (210 millimeters) from crown to rump and weigh more than 1 1/3 pounds (630 grams) at this stage of the pregnancy.  It should be noted that, with intensive medical care, babies born at this stage of the pregnancy may be able to survive.

Week 25:  During this week of your pregnancy, which is approximately 23 weeks after conception, the hands of the baby have fully developed, however, it should be noted that all of the nerve connections to the hands are still developing.  The mother may notice that exploration of the uterus has become an enjoyable task for the baby, as activity and movement levels have markedly increased by this stage of the pregnancy. 

Week 26:  During this week of your pregnancy, which is approximately 24 weeks after conception, the fingernails on the baby’s hands have developed.  There is also a significant level of development in the baby’s lungs.  The lungs are starting to produce a substance called surfactant, which serves to allow the air sacs of the lungs to inflate, while keeping them from sticking together and collapsing when they deflate.  Your baby may be more than 9 inches (230 millimeters) long from crown to rump and weigh nearly 2 pounds (820 grams) at this stage of the pregnancy.

Week 27:  This week of your pregnancy, which is approximately 25 weeks after conception, marks the end of the second trimester.  The primary developmental feature is the continuing maturation of the baby’s liver, lungs, and immune system.  The baby has also experienced an extensive growth spurt by this stage of the pregnancy, with the measurement from crown to rump having possibly tripled since the measurements that were noted in Week 12.

 

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By Jack Rambadt of Expecting Parents Alliance of America




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  • Pregnancy



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