Fetal Growth & Development: How Your Baby Grows
It is truly an amazing transformation. From a tiny fertilized egg (no bigger than the period at the end of this sentence) to a 7- 8 lb complete human being in a mere 280 days from the last menstrual period (approx 265 days from conception). There is no comparable miracle in all of nature. Below is a month by month guide to fetal growth and development.
Month 1 (0-6 weeks)
Following conception, the cells divide rapidly and begin to form primitive organs (spinal cord, heart, etc). The embryo is 1/4 inch in length by 4 weeks (10,000 times larger than at conception). The heart begins to beat. The placenta begins to grow and makes a hormone (HcG) that is used to diagnose pregnancy.
Month 2 (6-10 weeks)
The embryo is now 1 1/8 inch by 8 weeks. The heart is beating and functioning. The eyes, nose, and teeth buds are formed and the embryo starts to move it’s arms and legs. Organs (spinal cord, stomach, liver, kidneys, etc) are quickly developing in structure. An ultrasound performed at this time can see the embryo.
Month 3 (10-14 weeks)
The fetus is 2 1/2 to 3 inches long and weighs 1/2 to 1 oz. The hands, arms, legs, and toes are fully developed. Most organs have completed structural development but not all are functioning yet. Fetal movement can be seen on ultrasound (although not detected by the mother).
Month 4 (14-18 weeks)
The fetus is now 6-7 inches long and weighs 7 oz. The fingers and toes become more defined. The gender of the fetus can be clearly seen. The fetus exhibits reflex activity such as swallowing and the kidneys begin to make urine. The skin is thin and transparent.
Month 5 (19- 23 weeks)
The fetus has grown to 8-10 inches and now weighs 3/4 to 1 lb. Fetal hair begins to grow (including eyebrows and eyelashes) and fetal movement (“twitches”) may be felt by the mother. The organs continue to mature functionally but are still immature. Babies born at this time have a poor chance of survival.
Month 6 (24-28 weeks)
The fetus is now 12- 14 inches long and weighs 1 1/2 to 2 lbs. If born during this period, he/she has increasing chance for survival. Fetal hiccupping begins. Eye movement (opening and closing) begins. Babies can be seen on ultrasound sucking their thumbs.
Month 7 (28-32 weeks)
The fetus is now 14-17 inches long and weighs 2-3 1/2 lbs. The skin becomes less transparent as fat deposits develop under the skin and in other areas. Brain tissue is forming rapidly. He/She may respond to loud noises. Organs are almost fully mature except for the lungs. Cycles of sleep and wakefulness become more noticeable.
Month 8 (32-36 weeks)
The fetus has grown to 17-19 inches long and now weighs 3 1/2-6 lbs. This is the most rapid period of body growth. Hair follicles develop. If born, baby has excellent chance of survival. He/She begins to move down into the pelvis in preparation for birth.
Month 9 (36-40 weeks)
The fetus is now fully developed. He/She is 19-22 inches long and weighs 6-8 lbs. The lungs become mature and all organs are completely functioning. The head is deep into the pelvis, and false labor is common.
The signal that begins labor is still not fully understood. It is clear that the fetus “signals” the uterus through production of hormones and proteins. Under the influence of these products, contractions begin and the long and miraculous journey from those few cells to your healthy newborn baby is completed.