Fetal Development: Month 4

This is the fourth month of fetal development where aside from baby's monumental growth from the size of a pin head to about 5 inches at the end of this month, baby's vocal cords and intestines develop, as well as hair on baby's head and all over baby's body ( to keep baby nice and warm while baby's fat stores begin to build).

Week 13: Vocal Cords

Baby’s head is now half the size of baby’s crown to rump length. Inside baby’s head, new vocal cords are forming, and outside, tissue that will develop into bone is taking shape. Baby continues to move though you can’t feel anything yet. Flexing arms and kicking legs, and maybe even putting a newly formed thumb into the mouth may all constitute part of baby’s routine. Baby’s digestive system will see tiny intestines, up till now forming inside the umbilical cord, move towards the abdomen where they belong. More tissue for bone formation develops within the arms and legs, and tiny ribs are not far in the offing.

Week 14: Here Comes the Hair

At this fourth month of fetal development, hair starts to grow at the top of baby’s head, in baby’s eyebrows, and all over baby’s body. This fuzzy hair covering is called lanugo, a protective covering to keep baby warm and cozy inside your uterus. As baby develops fat deposits in the later stages of development, the lanugo will eventually fall off – but sometimes hangs on right up to birth. The hormones baby’s body has been producing start delivering more discernible changes, like a developing prostate gland for boys, or ovaries moving to the abdomen for girls. Baby’s intestinal tract starts producing meconium which is what baby’s first bowel movements will contain after birth. Baby’s mouth will also see its roof completely formed. Baby is now about the size of a small apple.

Week 15: Breathe, Suck, and Swallow

Baby has grown to about 4 inches and weighs about 3 ounces. This little one’s facial features continue to develop, with ears that have moved from the side of the neck to the side of the head and reached their final position. Eyes start moving from the side of the head to the front of the face. For babies who will have dark hair, hair follicles start producing pigment. All over baby, a nearly transparent skin is starting to form. Inside baby, bone and marrow continue to develop that tiny skeletal system, as baby kicks and flexes those little limbs. And at the end of the week, baby will be practicing breathing, sucking, and swallowing movements.

Week 16: Is that a Frown?

With facial muscles strengthening and developing, baby will begin to exhibit facial expressions like squinting and frowning. Baby can even make a fist now. How’s that for emotional expression? Baby’s back muscles are also stronger as fetal development progresses, so baby is able to straighten out more. Baby’s eyes, through still sealed eyelids, will begin to move from side to side and may show some sensitivity to light as eyelashes begin to form on those perfect little eyelids. Baby will become more sensitive to touch, can begin to feel pain, and may squirm if your belly is poked. And baby will start having hiccups, too.

Week 17: Baby Fat

This is the stage of fetal development where baby starts accumulating fat stores under skin that begins to turn translucent. Baby’s crown to rump length is approximately 5 inches and baby weighs in at approximately 5 ounces. Baby continues to practice sucking and swallowing movements, and baby’s heart rate becomes brain regulated (not spontaneous like it was during those early weeks) and ranges from 140 to 150 beats per minute, still about twice as fast as your own heart rate.



References:

Murkoff, Heidi and Sharon Mazel. What to Expect When You're Expecting. Workman Publishing Company, Inc. 2008

The Mayo Clinic. "Fetal Development." www.mayoclinic.com

The Westside Pregnancy Clinic. "Fetal Development." www.wpclinic.org




Return to Fetal Development
Return to Bright Baby Care Home Page