Having a baby is an amazing journey filled with fascinating developments and important milestones, starting from the moment that the egg is fertilized and ending with a brand new bundle of joy. But what, exactly, is going on in there? Join us as we take a closer look at what to expect from insemination to implantation to fetal development to childbirth.
Insemination – the First Step in Pregnancy
After sexual intercourse or artificial insemination, millions of sperm swim through the cervix into the uterus and then up into the two fallopian tubes, which connect each of a woman’s ovaries to her uterus. When an egg is released by one of the ovaries and is penetrated by a sperm cell, insemination has taken place and conception begins. The fertilized egg, now called a zygote, will have a full set of 46 chromosomes and the ability to become a whole new human being.
Implantation of the Fertilized Egg
After insemination, the zygote takes about five days to travel down the fallopian tube into the uterus, which now becomes the womb. Usually by the time the zygote reaches the womb, it has already divided into a ball of cells called a blastocyst (shown at left). The inner cells become the embryo and the outer cells will become the fetal support system during pregnancy. The new mother’s womb has been prepared for implantation by the hormones of her menstrual cycle. The blastocyst implants into the nourishing lining of the womb and becomes an embryo.
The Timeline of Pregnancy
Pregnancy is measured in weeks from the first day of the mother’s last period until childbirth. Pregnancy is also divided into a first trimester that includes weeks 1 through 12, a second trimester of weeks 13 through 26, and a third trimester of weeks 27 until childbirth. The process by which the cells of the embryo divide and begin to develop specific functions is called differentiation. The first trimester is considered the most critical time of a pregnancy because of the embryo’s rapid differentiation into specialized cells.
5 Weeks Into Pregnancy: Fetal Development
By this time the baby’s brain, spinal cord, heart, and gastrointestinal system have already begun to form, even though the embryo is only a quarter of an inch long. The embryo will start to develop arm and leg buds. The heart is beating regularly and blood is starting to move through rudimentary blood vessels. The beginnings of the structures that will become the eyes and ears are now forming.
8 Weeks Into Pregnancy: Fetal Development
At the end of six weeks, the fetal heartbeat may be seen and heard during a special test called a vaginal ultrasound. By seven weeks every one of the embryo’s essential organs has started to form. By the end of eight weeks the embryo begins to look like a little human and becomes a fetus. The fetus has begun to develop facial features and is the size of a bean.
12 Weeks Into Pregnancy: Fetal Development
The fetus’ face is now well formed, and the liver is actively making red blood cells. The arms and leg buds have now become longer and are recognizable limbs. Genitals appear to differentiate the sex of the fetus, which is now able to make a little fist. The head makes up about half of its body size and the fetus will close its eyes now until about week 28.
16 Weeks Into Pregnancy: Fetal Development
At 16 weeks you can almost see through the fetal skin, and a very fine growth of hair called lanugo is forming on the head. Muscles and bones are coming together to form the skeletal system. The fetus starts to move and make sucking motions with its mouth. The liver and pancreas have formed, and the intestines have started to make the first bowel movement, called the meconium.
20 Weeks Into Pregnancy: Fetal Development
By 20 weeks, the fetus is making itself known. What the mother felt as a slight fluttering at 18 weeks is now regular movement. The fetus can actually hear noises outside the womb. The heartbeat is loud enough to be heard with a stethoscope. Eyebrows and eyelashes have appeared and tiny nails have surfaced on the fingers and toes. The fetus is now about 8 inches long and 12 ounces in weight.
24 Weeks Into Pregnancy: Fetal Development
At 24 weeks the fetus is well on its way to being the little person that will emerge at birth. It is so attuned to its environment that the mother may feel the fetus move suddenly when it is startled by a loud noise. The eyes are now completely formed, and the all-important air sacs are beginning to form in the lungs. The fetus has even developed its own unique fingerprints and footprints.
32 Weeks Into Pregnancy: Fetal Development
By 32 weeks the fetus should weigh approximately four pounds and be about 11 or 12 inches long. At this point, if a mother were to give birth, a baby could survive with the help of medical technology. The lungs make rhythmic movements as they practice breathing air. The fetus has now developed its own sleep and wake cycles. The eyes may start to blink open and shut.
36 Weeks Into Pregnancy: Fetal Development
The fetus is now a baby getting ready for birth. Its skeletal system is still soft, but the baby has started to store calcium and iron. The skin begins to look like normal infant skin as the baby begins to gain weight and body fat. At 16 to 19 inches and 5 to 6 pounds, the baby will typically assume a head down position inside the womb in preparation for childbirth.
37 Weeks to Childbirth
After 38 weeks the infant is considered full term. The mother may actually notice a decline in baby movement because her little one has begun to run out of space in the womb. The fine lanugo hair has been replaced with normal scalp hair. The mother’s body pumps some final protective antibodies in through the placenta. The lungs are ready to take their first breath. Fetal development is complete. Childbirth is about to begin!