Prenatal Development A Month at a Time From Conception to Birth

Conception A sperm penetrates the egg’s protective membrane (left and center), then sheds its tail.

The Zygote After conception takes place, this single fertilized egg divides: into two identical cells, then four, then eight, then sixteen and so on.

WEEK 1 Early Pregnancy Factor 24 to 48 hours after fertilization begins, pregnancy can be confirmed by detecting a hormone called “early pregnancy factor in the mother’s blood (The test for this hormone, however, is not widely available). This substance helps prevent the mother’s immune system from rejecting the soon-to-be- implanted embryo and allows pregnancy to proceed.

Week 1 Implantation

The Zygote nestles into the well prepared endometrium – an event called implantation. This is the process whereby the early embryo embeds into the inner wall of the mother’s uterus. Implantation begins about 6 days after fertilization and is complete by about 12 days. Some of the cells will grow into the placenta: others will become part of the baby. With implantation, blood levels of the hormones progesterone rise in the mother.

Week 1-2 Approximately 8 days after fertilization, cells from the growing embryo begin producing a hormone called human chorionic gonadotropin or hCG. This hormone is present in a pregnant woman’s blood and urine almost immediately and is the substance detected by most pregnancy tests.

Week 1-2 Nutrients, oxygen, vitamins, and water in the mother’s blood stream pass through the placenta and umbilical cord to the embryo; while carbon dioxide and other waste flows back to the mother. The placenta also produces hormones and maintains fetal temperature above the mother’s temperature A twisting cord of blood vessels, called the umbilical cord, connects the embryo to the placenta.

Week 2-3 Stem cells have divided and differentiated into 3 different germ layers called Ectoderm, Endoderm, and Mesoderm. Each gives rise to major components of specific body structures and organs.

GERM LAYER Ectoderm Brain Spinal cord nerves Skin Nails Hair follicles Sweat glands Muscles & bone in face Endoderm Lining of respiratory Gastrointestinal Lungs Liver Pancreas Intestines

Germ Layers Cont Mesoderm Heart Kidneys Bones Muscles Blood vessels Reproductive Urinary

3-4 Weeks Only 3 weeks and 1 day after fertilization – the heart begins to beat. By 4 weeks, the heart typically beats between 105 and 121 times per minute. Upper and lower limb buds appear by four weeks

The Arms

Month 2 The Neural Tube In the 5 th week, the two ends of the long strip of cells that are the embryo fold in gently. One fold will become the head. Nerves that will become the brain have started to form. The fold at the other end of the embryo will become the genitals. Between these two folds are growing the neural tube (the site of the spinal cord) and a hint of the bones of the spine that protect the cord.

End of month 2 The next 3 slides show development at the end of the embryonic period. The fetus is in an amniotic Sac, filled with amniotic fluid. Notice the fingers are forming. The ragged chorionic villi outside the sac will form the placenta. The brain can be seen through the fine skin.

4-5 Weeks At this point, the embryo’s skin is only one cell thick. This makes the skin transparent, allowing us to see internal organs during early development WEEKS Embryo begins to move.

6-7 Weeks The embryo has brainwaves by 6 weeks, 2 days! Hiccups begin OLDEST BONES IN YOUR BODY=Bone formation begins between 6 and 7 weeks, starting with the clavicle, or collar bone, and the upper and lower jaw. This process is called ossification. By 7 weeks, the ovaries appear in the female embryo. In the male embryo, a gene on the Y- chromosome produces a substance causing the testes to begin to differentiate.

7-8 Weeks The embryo also kicks, and will jump if startled. By 8 weeks the brain is highly developed

End of Month 2 At the end of week 8, the embryo becomes a fetus, measuring about 1 ½ inches.

The Ear

8-9 WEEKS Thumb sucking begins and the fetus may swallow amniotic fluid 9-10 WEEKS By this point, ossification is underway in most bones. Fingers and toes, nails begin to emerge, as do fingerprints.

10-11 WEEKS The nose and lips are completely formed. Though gender is determined at fertilization, genitalia now distinguish male from female.

11-12 Weeks No diapers in the womb! = the fetus expels “waste” directly into the amniotic fluid. (But remember, the umbilical cord is also removing waste.)

Month 3 Nostrils, mouth, lips, teeth buds and eyelids form. Face is well formed. Head is half of fetus’s size. Eyelids fuse and do not open until 7 months. All organs are present, but immature. Genitals differentiate. Liver produces red blood cells Fetus is 2 1/2 – 3 inches long by end of month 3 and it weighs ½ oz.

Month 3

Month 4 Fetus can suck thumb, swallow, hiccup and move. Facial features are clearer Lanugo (fine hair) develops to help keep fetus warm Practices breathing Liver and pancreas produce fluids Skin is transparent Bones are getting harder

Month 4 Baby movement can be felt by mother, which is called quickening. The body proportions are more like a baby’s near the end of the 4 th month. The fetus is about 5 inches in length and 4oz by the end of the 4 th month.

Month 4

Month 5 Hair, nails, eyelashes and eyebrow appear Teeth continue to develop Organs keep maturing Fetus is active with increase muscle development Fetal heartbeat can be heard with a stethoscope Lanugo now covers body and collects Vernix- a waxy coating to cover and protect the skin.

Month 5 Mom definitely feels the baby Lower airways of lungs present, but not mature enough for gas exchange Baby will wake and sleep The nose and ears begin ossification and skeleton hardens Fetus is 6-7 inches long and about oz. by the end of month 5.

Month 5

Month 6 Fat is depositing under the skin Fetus looks wrinkled Eyes develop, eyelashes and brow well formed Can hear mom’s muffled talking, singing and rumbling of her stomach Air sacs in lungs mature but still can’t exchange gas, breathing movements begin Foot and finger prints form Fetus is 8-10 inches long and weighs 1 ½ -2 lbs

Month 6

Month inches long Weighs between 2 1/2 – 3 lbs Lanugo starts to disappear Can cry weakly Suck its thumb Make reflex movements: startle, grasp & swim movements Cerebral Hemispheres cover almost the entire brain

Month 7 Fetus is active, then rests Eyelids separate, open and close Nervous system is developed enough to control some body functions Respiratory system (breathing) developed

Month 8 Fetus may react to noises with a jerking actions Fetus has moved to “head down” position, but can turn back to “bottom down” Bones are fully developed but soft and pliable Rapid increase in the amount of body fat( ½ lb. a week)resulting in rapid weight gain Rhythmic breathing, however, lungs not fully mature. The baby can be inches long and weigh 4-6 lbs.

Month 8

Month 9 Fetal movements slow due to lack of room Continues with rapid weight gain Lanugo begins to disappear Hair is thick Skin is smooth no longer wrinkled. Baby acquires antibodies from mother Fetus descends into the pelvis and is ready for birth inches long and weighs 6-9 lbs.

Month 9 Birth! men

Birth 280 days (40 weeks) after the first day of the last menstrual period the baby is born.