When do fingernails develop on a fetus

Once it reaches the uterus, the morula becomes a blastocyst. The blastocyst then burrows into the uterine lining — a process called implantation. The sperm and egg unite in one of your fallopian tubes to form a one-celled entity called a zygote.

If more than one egg is released and fertilized or if the fertilized egg splits into two, you might have multiple zygotes. The zygote typically has 46 chromosomes — 23 from the biological mother and 23 from the biological father.

These chromosomes help determine your baby's sex and physical traits. Soon after fertilization, the zygote travels down the fallopian tube toward the uterus. At the same time, it will begin dividing to form a cluster of cells resembling a tiny raspberry — a morula.

The rapidly dividing ball of cells — now known as a blastocyst — has begun to burrow into the uterine lining endometrium. This process is called implantation. Within the blastocyst, the inner group of cells will become the embryo. The outer layer will give rise to part of the placenta, which will nourish your baby throughout the pregnancy. By the end of the fifth week of pregnancy — three weeks after conception — your hormone levels are rising.

The fifth week of pregnancy, or the third week after conception, the levels of HCG hormone produced by the blastocyst quickly increase. This signals your ovaries to stop releasing eggs and produce more estrogen and progesterone.

Increased levels of these hormones stop your menstrual period, often the first sign of pregnancy, and fuel the growth of the placenta. The embryo is now made of three layers. The top layer — the ectoderm — will give rise to your baby's outermost layer of skin, central and peripheral nervous systems, eyes, and inner ears. Your baby's heart and a primitive circulatory system will form in the middle layer of cells — the mesoderm.

This layer of cells will also serve as the foundation for your baby's bones, ligaments, kidneys and much of the reproductive system. The inner layer of cells — the endoderm — is where your baby's lungs and intestines will develop.

By the end of the sixth week of pregnancy — four weeks after conception — small buds appear that will become arms. Growth is rapid this week. Just four weeks after conception, the neural tube along your baby's back is closing.

The baby's brain and spinal cord will develop from the neural tube. The heart and other organs also are starting to form. Structures necessary to the formation of the eyes and ears develop. Small buds appear that will soon become arms.

Your baby's body begins to take on a C-shaped curvature. By the end of the seventh week of pregnancy — five weeks after conception — your baby's brain and face are the focus of development. Seven weeks into your pregnancy, or five weeks after conception, your baby's brain and face are growing.

Depressions that will give rise to nostrils become visible, and the beginnings of the retinas form. Lower limb buds that will become legs appear and the arm buds that sprouted last week now take on the shape of paddles. Eight weeks into your pregnancy, or six weeks after conception, your baby's lower limb buds take on the shape of paddles.

Fingers have begun to form. Small swellings outlining the future shell-shaped parts of your baby's ears develop and the eyes become obvious. The upper lip and nose have formed. The trunk and neck begin to straighten. By the end of the ninth week of pregnancy — seven weeks after conception — your baby's elbows appear.

In the ninth week of pregnancy, or seven weeks after conception, your baby's arms grow and elbows appear. Toes are visible and eyelids form. WEEK 6 8 weeks after the first day of the last normal menstrual period. WEEK 8 10 weeks after the first day of the last normal menstrual period.

WEEK 10 12 weeks after the first day of the last normal menstrual period. WEEK 12 14 weeks after the first day of the last normal menstrual period. WEEK 2 4 weeks after the first day of the last normal menstrual period Implantation begins the first week and the embryo continues to grow. Structures that will become arms and legs, called limb buds, begin to appear.

The brain develops into five areas and some cranial nerves are visible. The eyes and ear begin to form. Tissue forms that develops into the vertebra and some other bones. The heart continues to develop and now beats at a regular rhythm. There are numerous changes that occur during the embryonic stage.

First, the cells of the embryo called embryonic stem cells multiply and develop. They become the hundreds of different types of cells needed to make a whole human body.

The placenta forms during the embryonic stage. The placenta takes nutrients, oxygen, and water from your blood and passes these along to your baby through the umbilical cord. The placenta will filter out most of the harmful substances that may be present in your body.

The amniotic sac forms during this stage as well. It is filled with amniotic fluid, which surrounds and protects your baby in the uterus. By the end of the embryonic stage at week 10 of your pregnancy, your baby will be about 1 inch long. After the embryonic stage, the fetal stage begins and your baby is called a fetus. This stage runs from the 11th week until birth. Your baby will grow longer and gain weight quicker.

His or her organs and body parts will continue to develop. Fingernails and toenails begin to form and the kidneys start working. By the end of the first trimester, your baby has tripled in length to about 3 inches long. As your baby develops in the womb, your body goes through a lot of changes as well. He or she will be able to confirm your pregnancy. So much important development happens during the first trimester. It is important to not take any medicines without first asking the advice of your doctor.

March of Dimes: Pregnancy Week by Week. Last Updated: October 8,