What makes a fertilized egg attach to the uterus

The projections branch and rebranch in a complicated treelike arrangement. This arrangement greatly increases the area of contact between the wall of the uterus and the placenta, so that more nutrients and waste materials can be exchanged. The placenta is fully formed by 18 to 20 weeks but continues to grow throughout pregnancy. At delivery, it weighs about 1 pound. Merck and Co.

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This site complies with the HONcode standard for trustworthy health information: verify here. Common Health Topics. Development of the Blastocyst. Development of the Embryo. Development of the Fetus and Placenta. Normal Pregnancy. Test your knowledge. A breast lump mass is a thickening or bump that feels different from surrounding breast tissue. Which of the following statements about breast lumps is NOT correct? More Content. From Egg to Embryo Once a month, an egg is released from an ovary into a fallopian tube.

Placenta and Embryo at About 8 Weeks At 8 weeks of pregnancy, the placenta and fetus have been developing for 6 weeks. Allows materials to be exchanged between the blood of the mother and that of the embryo.

The embryo floats in fluid amniotic fluid , which is contained in a sac amniotic sac. Provides a space in which the embryo can grow freely. By 12 weeks of pregnancy: The fetus fills the entire uterus. By about 24 weeks: The fetus has a chance of survival outside the uterus. Was This Page Helpful?

Yes No. Physical Changes During Pregnancy. Development of the Fetus. Overview of the Postdelivery Postpartum Period. Hepatocellular Carcinoma. This arrangement does the following: Allows materials to be exchanged between the blood of the mother and that of the embryo Prevents the mother's immune system from attacking the embryo because the mother's antibodies are too large to pass through the membrane antibodies are proteins produced by the immune system to help defend the body against foreign substances The embryo floats in fluid amniotic fluid , which is contained in a sac amniotic sac.

Fertilization takes place in the fallopian tubes , which connect the ovaries to the uterus. Fertilization happens when a sperm cell successfully meets an egg cell in the fallopian tube.

Once fertilization takes place, this newly fertilized cell is called a zygote. From here, the zygote will move down the fallopian tube and into the uterus. The zygote then burrows into the uterus lining. This is called implantation. An exception to this rule would happen with in vitro fertilization IVF. In this case, eggs are fertilized in a lab. Ovulation is when a mature egg is released from one of your ovaries. There are a number of reasons why fertilization might not happen.

This includes use of contraception and infertility. Usually, only one egg is released during ovulation. However, the ovaries sometimes release two eggs at once. In this case, you might become pregnant with twins. These twins will be known as fraternal twins also called nonidentical twins.

Fertility treatments like IVF can increase the likelihood of multiple births , according to Cleveland Clinic. This is because fertility treatments often involve transferring more than one embryo to the uterus at a time to increase the chances of pregnancy.

Fertility drugs can also result in more than one egg being released during ovulation. Because both cells come from the exact same egg cell and sperm cell, identical twins will have the same DNA, the same sex, and a nearly identical appearance. At the point of ovulation, the uterus wall is thick. The American College of Obstetrics and Gynecology ACOG considers someone pregnant only once the embryo is successfully implanted against the uterine wall.

In other words, implantation marks the beginning of a pregnancy. The embryo, however, might not implant. Emergency contraception , intrauterine devices IUDs , and infertility could prevent the embryo from implanting. Also, don't take any prescription or over-the-counter drugs without checking with your doctor to ensure they're safe to use during pregnancy.

By four weeks, the embryo is made up of three distinct layers. The inner layer will gradually develop into the lungs, liver and digestive system; a middle layer will be the baby's bones, muscles, kidneys, heart, and sex organs; and an outer layer will eventually form the skin, hair, eyes, and nervous system.

By the end of the second week after fertilization, you may also begin to experience the first signs of morning sickness.

About 70 percent of all pregnant women have some traces of morning sickness, but the severity of the condition can vary from mild nausea to daily bouts of violent vomiting.

For some women, symptoms are not confined to the morning, either: many complain of a rocky stomach at the end of the day. Experts believe that morning sickness is caused by the increase in hormones coursing through the system of a pregnant woman. You may also feel more fatigue than usual: Many women feel extremely tired during their first trimester of pregnancy.

Experts attribute this fatigue to the additional work your body has to do, now that it is making a baby. Your blood flow has increased to accomplish the job of feeding your baby. As a result of the increased blood flow, your heart has to pump harder and your cardiac volume will increase by as much as 50 percent. If your test shows that you're pregnant, congratulations! This is an exciting and joyous time, but it can be overwhelming as well.

Don't be surprised if you are feeling a range of emotions, including apprehension and confusion. It will help to learn all you can about pregnancy and the steps you need to take care of yourself -- and your unborn child.

March of Dimes. Placenta Previa. Howard Hughes Medical Institute. Developmental Biology. Holy Name Hospital. Health Manual: Pregnancy and Childbirth. The First Trimester Weeks.