Pregnancy and Pregnancy and Fetal Fetal DevelopmentDevelopment

I. Fertilization – (conception), I. Fertilization – (conception), occurs in the fallopian tubeoccurs in the fallopian tube

Fusion of 2 haploid gametes to form a zygote Fusion of 2 haploid gametes to form a zygote (sperm and egg)(sperm and egg)

Even though over 200 million sperm are Even though over 200 million sperm are introduced into the female repro system, only introduced into the female repro system, only about 10,000 reach the uterine tube and fewer about 10,000 reach the uterine tube and fewer than 100 reach the isthmus (middle) of the tube.than 100 reach the isthmus (middle) of the tube.

Did you know? Only 1 sperm fertilizes an oocyte Did you know? Only 1 sperm fertilizes an oocyte but dozens are needed to disrupt the layers of but dozens are needed to disrupt the layers of cells that surround the oocytecells that surround the oocyte

Why can’t more than one sperm fertilize an egg? Why can’t more than one sperm fertilize an egg? Because enzymes are released to inactivate the Because enzymes are released to inactivate the sperm and harden the area around the egg.sperm and harden the area around the egg.

II. Stages of DevelopmentII. Stages of Development pregnancy is approx 40 weeks (9 months) long and pregnancy is approx 40 weeks (9 months) long and

divided into 3 stages:divided into 3 stages: First Trimester-(Month 1, 2, 3) the most important First Trimester-(Month 1, 2, 3) the most important

development occurs in this stage.development occurs in this stage. Weight – 150mg to 14 g (.49 oz)Weight – 150mg to 14 g (.49 oz) Diameter - .005 inch- 3 inchesDiameter - .005 inch- 3 inches Rudimentary organs formRudimentary organs form Cell (blastocyst) must implant into the endometrium 7 to Cell (blastocyst) must implant into the endometrium 7 to

10 days after fertilization10 days after fertilization Placenta develops from blood cells that surround the Placenta develops from blood cells that surround the

embryo, this will allow the exchange between the embryo, this will allow the exchange between the maternal and embryonic circulationmaternal and embryonic circulation

Umbilical cord- connects the mom to the embryoUmbilical cord- connects the mom to the embryo

Stages of Development Stages of Development (cont)(cont)

Second Trimester (Month 4, 5, 6)Second Trimester (Month 4, 5, 6) Weight- by the end of this trimester the Weight- by the end of this trimester the

fetus weighs approx .64 kg (1.4 lbs)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 bestUsually when the female feels her best

Third Trimester (Month 7, 8, 9)Third Trimester (Month 7, 8, 9) Weight- fetus undergoes the largest weight Weight- fetus undergoes the largest weight

gain; by the end the fetus weight 5.5 to 8 lbsgain; 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 Most organs become fully developed and

functioning (except for lungs)functioning (except for lungs)

III. Maternal ChangesIII. Maternal Changes

Respiratory rate and tidal volume Respiratory rate and tidal volume increases (fetus needs oxygen)increases (fetus needs oxygen)

Blood Volume increases- by the end of Blood Volume increases- by the end of pregnancy, blood volume has increased pregnancy, blood volume has increased by almost 50%by almost 50%

Filtration rate increases - this Filtration rate increases - this corresponds to increased blood volume corresponds to increased blood volume and metabolic processesand metabolic processes

Uterus increases in sizeUterus increases in size Mammary glands increase Mammary glands increase

IV. The Three Stages of IV. The Three Stages of LaborLabor

Dilation- the cervix dilates and the baby Dilation- the cervix dilates and the baby moves towards the birth canalmoves towards the birth canal When uterine contractions beginWhen uterine contractions begin Usually when the water breaks Usually when the water breaks

(amniochorionic membrane ruptures)(amniochorionic membrane ruptures) Expulsion- when the infant arrives into Expulsion- when the infant arrives into

the outside worldthe outside world Placental – usually within the hour of Placental – usually within the hour of

giving birth to the infant, the placenta is giving birth to the infant, the placenta is ejected ejected