Pregnancy and Fetal Development

I. Fertilization – (conception), occurs in the fallopian tube Fusion of 2 haploid gametes to form a zygote (sperm and egg) Fusion of 2 haploid gametes to form a zygote (sperm and egg) Even though over 200 million sperm are introduced into the female repro system, only about 10,000 reach the uterine tube and fewer than 100 reach the isthmus (middle) of the tube. Even though over 200 million sperm are introduced into the female repro system, only about 10,000 reach the uterine tube and fewer than 100 reach the isthmus (middle) of the tube. Did you know? Only 1 sperm fertilizes an oocyte but dozens are needed to disrupt the layers of cells that surround the oocyte Did you know? Only 1 sperm fertilizes an oocyte but dozens are needed to disrupt the layers of cells that surround the oocyte Why can’t more than one sperm fertilize an egg? Because enzymes are released to inactivate the sperm and harden the area around the egg. Why can’t more than one sperm fertilize an egg? Because enzymes are released to inactivate the sperm and harden the area around the egg.

II. Stages of Development pregnancy is approx 40 weeks (9 months) long and divided into 3 stages: pregnancy is approx 40 weeks (9 months) long and divided into 3 stages: First Trimester-(Month 1, 2, 3) the most important development occurs in this stage. First Trimester-(Month 1, 2, 3) the most important development occurs in this stage. Weight – 150mg to 14 g (.49 oz) Weight – 150mg to 14 g (.49 oz) Diameter inch- 3 inches Diameter inch- 3 inches Rudimentary organs form Rudimentary organs form Cell (blastocyst) must implant into the endometrium 7 to 10 days after fertilization Cell (blastocyst) must implant into the endometrium 7 to 10 days after fertilization Placenta develops from blood cells that surround the embryo, this will allow the exchange between the maternal and embryonic circulation Placenta develops from blood cells that surround the embryo, this will allow the exchange between the maternal and embryonic circulation Umbilical cord- connects the mom to the embryo Umbilical cord- connects the mom to the embryo

Stages of Development (cont) Second Trimester (Month 4, 5, 6) Second Trimester (Month 4, 5, 6) Weight- by the end of this trimester the fetus weighs approx.64 kg (1.4 lbs) Weight- by the end of this trimester the fetus weighs approx.64 kg (1.4 lbs) Length- 230 mm (9 in) Length- 230 mm (9 in) Growth period Growth period Usually when the female feels her best Usually when the female feels her best Third Trimester (Month 7, 8, 9) Third Trimester (Month 7, 8, 9) Weight- fetus undergoes the largest weight gain; by the end the fetus weight 5.5 to 8 lbs Weight- fetus undergoes the largest weight gain; by the end the fetus weight 5.5 to 8 lbs Length 346 mm (13.5 in) Length 346 mm (13.5 in) Most organs become fully developed and functioning (except for lungs) Most organs become fully developed and functioning (except for lungs)

III. Maternal Changes Respiratory rate and tidal volume increases (fetus needs oxygen) Respiratory rate and tidal volume increases (fetus needs oxygen) Blood Volume increases- by the end of pregnancy, blood volume has increased by almost 50% Blood Volume increases- by the end of pregnancy, blood volume has increased by almost 50% Filtration rate increases - this corresponds to increased blood volume and metabolic processes Filtration rate increases - this corresponds to increased blood volume and metabolic processes Uterus increases in size Uterus increases in size Mammary glands increase Mammary glands increase

IV. The Three Stages of Labor Dilation- the cervix dilates and the baby moves towards the birth canal Dilation- the cervix dilates and the baby moves towards the birth canal When uterine contractions begin When uterine contractions begin Usually when the water breaks (amniochorionic membrane ruptures) Usually when the water breaks (amniochorionic membrane ruptures) Expulsion- when the infant arrives into the outside world Expulsion- when the infant arrives into the outside world Placental – usually within the hour of giving birth to the infant, the placenta is ejected Placental – usually within the hour of giving birth to the infant, the placenta is ejected