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The Monthly Development of a Baby in Womb

By Kristin Davis ; Updated June 13, 2017

Your baby will grow each day of your pregnancy, starting as embryonic cells and, before you know it, becoming the size of a full-term baby ready to meet her new world. Monthly prenatal visits with your obstetrician or midwife will help ensure your baby is growing and developing properly.

Keeping Track

Each month your baby develops in the womb he will grow and gain weight. While some babies grow faster than others, there are normal ranges for growth and development, according to the American Congress of Obstetricians and Gynecologists. At scheduled prenatal visits, your doctor can monitor the growth and development of your baby while he’s in your womb to ensure he is on track and to avoid possible complications.

Time Frame

Trimesters are three months long, and an expectant mom and new baby will coexist as one for three trimesters, or nine months, according to KidsHealth. By the end of each trimester, your baby will be much larger than the previous trimester and will be able to do new things.


At the beginning of your pregnancy, your baby is less than an ounce in weight and about a half-inch in length. In the second month, she will still weigh less than an ounce but will double in length to an inch. In your third month, your baby will finally weigh a little more than 1 oz. and will approximately triple in size to about 3 1/2 inches.

By the end of your second trimester, or the six-month mark, your baby will quadruple in length from the third month to approximately 12 inches and will weigh 1 to 1 1/2 lbs.

During the last three months, your baby will grow even more rapidly than previous months. In the seventh month of pregnancy, your baby will weigh about 2 1/2 lbs and will be about 14 inches long. During the eighth month, she will weigh around 5 pounds and be about 18 inches long. Just before birth, your baby will weigh between 6 and 9 pounds and be approximately 20 inches long.


Your baby’s heart will begin to beat by the end of the first four weeks of pregnancy. During the second month, genitals will begin to form as will eyelids, but his eyelids will remain closed until later. In the third month, he will begin to form soft nails as his fingers and toes continue to grow. The fourth month begins the period where he can hear and swallow in the womb and he will begin to develop eyebrows and eyelashes. In the fifth month, your baby can suck his thumb, and wake and sleep regularly, and you can begin to feel him kick as he becomes more active. During the sixth month, your baby will start to grow hair, his brain begins to develop and he starts to open and close his eyes. In the seventh month, he can recognize light when his eyes open and can respond to sounds by moving around. During the eight month, he can hiccup and his bones begin to harden. In the last month of pregnancy, your baby gets ready for birth by turning his head into a downward position, and he’ll gain about a half-pound per week.


From the time of conception, your baby will alter your body, according to the American Congress of Obstetricians and Gynecologists, and you will require more rest and nutrients. Speak with your caregiver for recommendations for a balanced diet and about prenatal vitamins.

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