1 Prenatal Development

2 Notes:  Prenatal refers to the period of time before birth. It is during this 40 week period (about nine months) that one cell develops into a human infant. The prenatal development begins immediately as the mother conceives (the sperm meets the egg).

3 Review: The 3 stages of prenatal development  1) Germinal Stage: (Period of the zygote) First 2 weeks of pregnancy First 2 weeks of pregnancy  2) Embryonic Stage: (Period of the Embryo) 3 rd to 8 th week of pregnancy 3 rd to 8 th week of pregnancy  3) Fetal Stage: (Period of the fetus) 9 th week to end of pregnancy/birth 9 th week to end of pregnancy/birth  *They occur in the above order

4 Conception  Each month a woman’s ovary releases a cell or egg called the ovum. The egg moves from the ovary into the Fallopian tube and into the uterus. This travel takes about two to three days.  If the egg reaches the uterus before it meets a sperm it is flushed away with the woman’s menstrual flow. However, if the egg is fertilized before it reaches the uterus then it will implant itself in the uterine wall. The egg can only be fertilized in the Fallopian tube. If the egg does become fertilized in the Fallopian tube then it is at this point that a woman had conceived.

5 Period of the Zygote  The period of the ovum/germinal/zygote stage is the first stage in the life of a human baby. This stage lasts for approximately two weeks immediately after conception.  When the fertilized egg reaches the uterus, it attaches itself to the uterine wall; the thickened lining of the uterus that is shed through menstruation if the woman has NOT conceived, and begins to grow. The lining in the uterus is used to nourish the fertilized egg. The egg grows by a process called cell division. The single cell divides and becomes two, two become four, four become eight and so on until there are millions of cells. Each cell is preprogrammed to become the skin, the bones, the hair, etc of the baby. At the end of this two week period the ovum is still only the size of a pinhead.

6 Period of the Embryo  The second stage of life is the period of the embryo and it lasts for about six (6) weeks. The embryo becomes firmly attached to the inner lining of the uterus. By the end of this stage the connecting tissue between the embryo and the lining becomes the placenta. The placenta provides nourishment and oxygen from the mother’s blood stream to the embryo through the umbilical cord.  The growing embryo is soon surrounded by a bag of liquid called amniotic fluid which acts like a cushion to protect it through minor bumps or falls of the mother. The baby remains in this sac of liquid until just before birth. It is the amniotic sac that breaks when women refer to their “water breaking.”

7 Period of the Fetus  The period of the fetus is the third and last stage of development of the baby, during pregnancy. The embryo becomes a fetus around the 8 th -9 th week of pregnancy until the end of the pregnancy. It is during this period that the unborn baby becomes more recognizable; with legs, arms, sex organs, even fingers and toes. While all the internal organs are present at the beginning of this period, they are not all yet functioning.

8 Period of the fetus Cont’d  Between the fourth and fifth month of pregnancy the fetus’s movements touch the wall of the uterus. The feeling the mother gets with these initial movements is sometimes called “quickening” as it is now apparent to the mother that she has life inside of her. However, the baby has actually been active long before this. By knowing when the expecting mother first felt life the doctor can better determine the baby’s fetal age and its birth date.

9 Period of the Fetus Cont’d 2  The unborn baby can suck its thumb, cough, sneeze, yawn and suffer hiccups. It can also cry, although you can not hear it. During the ninth month of prengnancy the baby’s weight will shift suddenly. This allows the mother to feel more comfortable. This movement is called “lightening.” This means that the baby has dropped into the lower pelvis and is ready for delivery (head down).

10 Ready for Birth  The baby is now turned head down in the lower pelvis and is ready to be born.

11 Breech babies  Breech babies present with their bottoms down and their heads up. When a woman is 28 weeks pregnant, her baby has a 25% chance of being in the breech position. As the pregnancy progresses, the likelihood of a baby staying in the breech position gets smaller. At 33 weeks of pregnancy there is around a 5% chance of a breech presentation. At full- term around 3-4% of babies remain in the breech position. There are different types of breech babies and they are described by the position that they are in. There is the ‘complete breech’ which is where the baby sits cross legged. The “frank breech” where the baby’s legs are straight and held flat against his/her body. There is the rare ‘footling breech’ where the baby’s foot or feet are coming first (before their bottom). There is the very rare ‘kneeling breech’ where the baby is in a kneeling position.