By pregnancy week 4 the body starts producing high levels of human chorionic gonadotrophin (HCG). This happens after successful conception. High levels of HCG are necessary to sustain pregnancy.

Development of the baby

At pregnancy week 4 the cells divide and multiply rapidly and three layers of cells are formed:
A. The outer layer (the ectoderm) develops into the baby's brain, nervous system, skin, hair, nails and teeth.
B. The middle layer (the mesoderm) becomes the heart and blood vessels, bones, muscles and reproductive organs.
C. The inner layer (the endoderm) develops into the lungs, liver, bladder and digestive system.

The cells of the embryo grow lengthwise. Each of the embryo's body cells has 46 chromosomes in 23 pairs with one of each pair inherited from each parent. Each new cell has the same number of chromosomes and the same genetic information. This pregnancy week 4 the baby's amniotic cavity starts forming. From this cavity the placenta grows and nourishes the baby throughout the pregnancy. The placenta is very important for the baby's health and well being during the pregnancy week by week. The placenta comprises of vascular networks and blood that carry oxygen and vital nutrients to the baby. The blastocyst gets to the uterus, and settles down. The blastocyst burrows itself into the lining of the uterus called as implantation.

During pregnancy week 4 the baby's vital organs begin to take shape. It is more important that from pregnancy week 4 a woman starts avoiding her body or the baby exposed to harmful substances. Many harmful substances like tobacco and alcohol for babies can be fatal and cause deformities. By pregnancy week 4 the mother might start feeling a little bit pregnant. The most common symptom most women experience is increasing fatigue and mood swings. Others might feel some mild abdominal cramping in early pregnancy.

Many women happen to find out if they are pregnant by 4 weeks. A home pregnancy test is sufficient for determining pregnancy. If a test is taken and it is found that it turns out to be positive i.e. a woman is pregnant, she should call her healthcare provider. The healthcare provider can also prescribe a prenatal vitamin if not started yet.

What to eat

There are numerous foods that a woman should avoid while being pregnant. She should try and avoid eating soft cheese and smoked or raw seafood. This is because many of these bacteria that can cause fetal damage or might also lead to a miscarriage.

Healthy surroundings

Environmental pollutants are just as harmful as other toxins which might be ingested during pregnancy. It is important that a woman is aware of any environmental toxins and pollutants that may harm her fetus during pregnancy. Some of the common pollutants that can affect fetal development include: lead, mercury, pesticides and PCBs. Some women are exposed to certain PCBs at work which are a mixture of chemical compounds. In an environment where a variety of chemicals are used, should be avoided and should be checked with the healthcare provider to ensure that the work environment is safe enough.