Your Developing Baby: Conception To Birth

Every pregnancy and every expectant mother and unborn baby is different, so the following information should only be used as a “general” guide for healthy pregnancy development, and should not replace information provided by your physician.

Most references on trimester charts are typically found to be in gestational age rather than fetal age. We added both here so it would be clearer to you regarding what developmental period you are in. Measurements shared are in total length from baby’s head to toe, but again everyone’s pregnancy and measurements are different so this is just a “general” guide.

Week 1 & 2

This is when conception begins. The sperm penetrates the egg and a creates a zygote. A single zygote consists of 46 chromosomes. After traveling through the fallopian tube it divides into several cells and eventually rests in the uterus. About one week to ten days after conception, it is imbedded in the uterine lining and this essentially begins the embryonic stage.

Week 3

Fetal Age: 1 Week
The embryo’s brain, heart, spinal cord and gastrointestinal tract is beginning to develop.

Week 4 & 5

Fetal Age: 2 & 3 Weeks
The heart is beating and the placenta has begun to form. The embryo is about ¼ inch at this period. Arm and leg buds may be slightly visible.

Week 6

Fetal Age: 4 Weeks
An internal ultrasound inserted through the vagina may be able to detect a heart beat. The embryo is approximately ½ inch. The embryo’s lungs, eyes and nose begin to develop at this state and the fingers and toes appear webbed.

Week 7

Fetal Age: 5 Weeks
Hair follicles are developing and tongue and eyelids as well. At this period, the main organs have started forming.

Week 8

Fetal Age: 6 Weeks
This tiny embryo now has everything present that a human body requires. Facial features such as ears and eyelids are becoming more developed. It is near the end of the embryonic period and now will begin the fetal period. Approximately 1 inch at this stage.

Weeks 9 thru 12

Fetal Age: 7 thru 10 Weeks
Now known as the fetus, it has grown more rapidly measuring approximately 3 inches in length and weighing about one ounce. It is now clear whether the fetus is male or female though difficult to identify via a typical ultrasound.

You may also request a FREE information packet by calling us directly, toll free, at 1-866-691-3300 or 716-639-3900; or, email Adoption STAR’s Birth Parent Department.