First six weeks
Your fertilized egg becomes a ball of cells (known as a blastocyst), which floats into your uterus and implants itself in the lining. The basis for your baby's future development is now laid down.
Your baby at six weeks of pregnancy
© DK
Your baby's progress
Once it has implanted, the embryo begins to make chemicals that have two functions. First, they signal to your body that the embryo has arrived and this triggers changes in your body: your ovulation cycle stops; the mucus in your cervix thickens; your uterine wall softens; and your breasts begin to grow. Second, your immune system is suppressed so that the embryo is not treated as foreign and rejected, but is allowed to grow. Also, an outer layer of the ball of cells becomes a protective cocoon around the embryo. This cocoon will create the beginnings of the placenta and the support system in which the embryo will grow: the amniotic sac (the watery balloon in which it will float) and the chorion (a safety cushion around the amniotic sac). The yolk sac (which will make blood cells until the liver takes over) forms from the inner layer. The chorion grows finger-like projections, the chorionic villi, with which the cocoon burrows into your uterine lining.
The cells specialize
Throughout these early weeks, the embryo's cells become more specialized. There are now three layers of them. Each layer will create different organs of your baby's body. The innermost layer makes a primitive tube that later develops into the lungs, liver, thyroid gland, pancreas, urinary tract, and bladder. The middle layer will become the skeleton, muscles (including the heart muscle), testes or ovaries, kidneys, spleen, blood vessels, blood cells, and the deepest layer of skin, the dermis. The outer layer will provide the epidermis, sweat glands, nipples (and breasts, if your baby is a girl), hair, nails, tooth enamel, and the lenses of the eyes.
The embryo's support system
The villi, finger-like projections, of the growing placenta intermingle with the mother's blood vessels in the uterine wall in such a way that they eventually become surrounded by “lakes” of blood. The mother's blood flows in and around these spaces and, because it is divided by only a cell or two from fetal blood, exchange of nutrients and waste between fetus and mother can take place in these blood spaces. The placenta is a hormone factory pumping out hormones, such as human chorionic gonadotrophin (hCG), that support a healthy pregnancy. Until the sixth week, the embryo's blood cells are supplied by the yolk sac. After the end of the third week, the blood circulation is pumped by the baby's own heart. Until week eight the baby is known as an embryo, after which it is called a fetus, Latin for “young one”.
Mothers during the first six weeks
At the end of the first month, you probably won't be sure that you're pregnant, although you may have your suspicions.
Symptoms
You'll notice few, if any, symptoms, although you may feel slightly premenstrual and pass urine more often than usual. Your breasts may feel sore and heavy and your nipples may tingle. You may even feel sick.
Ovulation cycle
Once the embryo has implanted on the lining of your uterus, your normal cycle stops. The corpus luteum in the ovary continues to make progesterone, which prevents you having periods and keeps the pregnancy healthy and viable.
Cervix
The hormone progesterone makes your cervical mucus thicker, forming a plug. This stays in place until the end of your pregnancy, when it comes out (the show).
Uterus
The wall of your uterus softens so that the embryo can become firmly embedded. Your uterus starts to get bigger almost from the moment of implantation.
Baby
Probably even before you know you're pregnant, the embryo reaches a critical stage in development so it's vital to plan for pregnancy.
Spinal cord
During the second week of life, a dark mark appears on the embryo's back. This marks the position of the spinal cord.
Heart
By the end of the third week, the embryo has a heart that's now beginning to beat.
Sensitivity
In the third week, the embryo enters a sensitive phase of development when all the major organs are forming. Embryos are generally robust but can be harmed by drugs, alcohol, smoking, infections, and so on.
Posted 30.06.2010
Get more on this subject…
