The First Trimester

Week 1 & 2 Gestational Age

Your period has just ended, and your body is getting ready for ovulation. For most women, ovulation takes place about 14 days before the start of your next period. During intercourse, several hundred million sperm are released in the vagina. Sperm travel through the cervix and into the fallopian tube, where the female’s eggs are. If a sperm penetrates, conception occurs and creates a single set of 46 chromosomes called a zygote, which is the basis for a unique new human being. The fertilized egg travels down the fallopian tubes and implants into the wall of the uterus where it begins to grow and thrive.

Week 3 Gestational Age

The embryo is going through lots of basic growth at this time, with the beginning development of the brain, spinal cord, heart, and gastrointestinal tract.

Week 4 & 5 Gestational Age

Arm and leg buds are visible. The heart can now beat at a steady rhythm. The early structures that will become the eyes and ears are forming. The placenta forms as a safe and nurturing home for the embryo as it grows. A pregnancy test can often accurately show positive results at this point.

Week 6 Gestational Age

The formation of the lungs, jaw, nose, and palate begin. The hand and feet buds have webbed structures that will become fingers and toes. The brain continues to form. A vaginal ultrasound may detect an audible heartbeat. The embryo is about a ½ inch in length.

Week 7 Gestational Age

Every essential organ has begun to form in the embryo’s tiny body. Hair and nipple follicles are forming, and the eyelids and tongue have begun forming, as well. The elbows and toes are more visible as the trunk or torso begins to straighten out.

Week 8 Gestational Age

The ears continue to form externally and internally. Everything that is present in an adult human is now present in the small embryo. The bones begin to form, and the muscles can contract. Facial features continue to mature, and the eyelids are more developed. The embryo now begins the fetal period. The embryo is about 1 inch long and is the size of a bean.

Weeks 9 thru 13 Gestational Age

The fetus has grown to about 3 inches in length and weighs about an ounce. The genitals have clearly formed into male or female, but still cannot be seen clearly on an ultrasound. The fetus can make a fist, and the buds for baby teeth appear. The head is nearly half the size of the entire fetus.