Fetal Development During The Second Trimester

Pregnancy and fetal development have characteristic and predictable stages that can be seen or not seen, felt or not felt, and understood or not understood.  After fertilization the embryo quickly begins to grow, change, and show characteristic signs and stages of human development.  During the 40 weeks of gestation a single cell develops into an embryo consisting of thousands of cells and culminating in the delivery of a fully formed infant.  Here are presented the changes seen in fetal development during the second trimester.

14 weeks development:

At the start of the second trimester most of the baby’s organs have formed.  Your baby is clearly identifiable as a baby and fetal movement can be detected during an ultrasound.  The neck becomes more defined, and the head is erect.  The arms and legs are developed; the baby’s eyes start to face forward and slowly move.  The ears continue to migrate to their final position.

• Your baby is about the size of a peach.
• Length:  About 3.42 inches

15 weeks development:

Your baby is growing rapidly, and bones development continues and will be visible on ultrasound images.  Your baby may be able to make sucking motions with his/her mouth.  Your baby’s scalp and hair patterns are forming.

• Your baby is about the size of an apple.
• Length:  About 3.98 inches

16 weeks development:

Your baby’s limb movements become more coordinated.  Your baby will be moving; however, the movements likely will not be felt by you.  The skin is pink and transparent.  The ears are almost fully formed and there is some evidence the baby can now hear.

• Your baby is about the size of an avocado.       
• Length: About 4.57 inches

17 weeks development:

Toenails begin to develop.  Your baby is becoming more active in the amnionic sac, it is not uncommon for your baby to roll and flip.  Your baby’s heart is beating rapidly and pumps about 100 pints of blood each day.        

• Your baby is about the size of a pear.
• Length:  About 5.12 inches

18 weeks development:

At this stage of development all organs and structures have been formed.  Your baby’s digestive system has started working and respiratory movements occur.  The lungs are developed; however, they have not developed enough to permit survival outside of the uterus.

• Your baby is about the size of a sweet potato.
• Length:  About 5.59 inches

19 weeks development:

Growth has slowed.  A greasy or cheese like coating begins to cover your baby.  It is called vernix.  The vernix helps protect the skin from abrasions, chapping, and hardening that can occur after lengthy exposure to amnionic fluid.  For girls, the uterus and vaginal canal are forming.

• Your baby is about the size of a mango.
• Length: About 6.02 inches

20 weeks development:

The halfway point!  Your baby’s movements become stronger and more frequent.  You will likely feel them.  The movements are referred to as quickening.  In many instances the mother’s first awareness of movement or “kicks” will be the 20-week mark. Your baby has fingernails, toenails, and maybe some head and body hair.

• Your baby is about the size of a banana.
• Length:  About 6.46 inches

21 weeks development:

Your baby is completely covered with a fine, silky hair called lanugo.  This layer of hair helps hold the protective vernix on the skin.  It is common that at 21 weeks your baby is able to suck his/her thumb.  Eyebrows and eyelashes appear.

• Your baby is about the size of a carrot.
• Length:  About 10.51 inches

22 weeks development:

The lungs continue to develop, hair is much more visible, and your baby is starting to develop regular sleeping and waking times.  For boys, the testes have begun to descend.

• Your baby is about the size of a papaya.
• Length:  About 11 inches

23 weeks development:

Your baby is developing rapid eye movements.  Skin ridges appear on the palms and soles; these are the foundation for fingerprints and footprints.  You may feel jerking movements; your baby likely has the hiccups.

• Your baby is about the size of an eggplant.
• Length:  About 11.38 inches

24 weeks development:

Your baby’s skin is wrinkled, translucent, and may appear to be red because the baby’s blood is visible in surface capillaries.  The tone of skin color at this time of development may vary depending on your baby’s ethnicity, however, in most cases the skin appears red.

• Your baby is about the size of an ear of corn
• Length:   About 11.81 inches

25 weeks development:

Your baby might respond to familiar sound with movement.  Examples of such sounds are your voice or frequently played music.  Most of the time your baby is sleeping and experiencing rapid eye movement (REM).  This means the eyes are moving even though the eyelids are closed.

• Your baby is about the size of an acorn squash.
• Length:  About 13.62 inches

26 weeks development:

At this stage of development your baby’s lungs are beginning to produce surfactant.  This is a substance that allows the air sacs in the lungs to inflate and keep them from sticking together and collapsing when they deflate or exhale.  A baby born at this stage of development has an excellent chance of survival outside of the uterus due to the many advances in neonatal intensive care delivery systems.

• Your baby is about the size of a zucchini.
• Length:   About 14.02 inches

The information is presented to be a general guide to present the events surrounding fetal development.  It is for informational purposes only.  The information provided is not intended to be the only information available concerning fetal development during the second trimester.  The material provided is not expected to be a substitute for advice or information from your physician or health care provider.

If you have any questions, concerns, apprehensions, unease, or worry about your fetus’ development contact your health care provider immediately.