Fetal Development and Childbirth Notes

Fetal Development (Weeks 9-38)

  • Conceptus officially called a fetus.

  • Nutrients primarily from the placenta, notuterine milk (as in the preembryonic period).

Placentation (Placenta Formation)

  • Connection between mother and baby.

  • Begins at implantation but proliferates during the fetal period.

  • Structures Involved:

    • Chorion: Outer membrane, early placenta development.

    • Yolk sac.

    • Umbilical cord: Connection point.

    • Amnion: Forms amniotic sac with amniotic fluid.

    • Allantois.

  • Umbilical Cord:

    • Connects mom and baby at the umbilicus (belly button).

    • Contains Wharton's jelly: Soft connective tissue for insulation.

    • Umbilical arteries: Carry deoxygenated blood from fetus to placenta.

    • Umbilical vein: Carries oxygenated blood from placenta to fetus.

Maternal-Fetal Blood Exchange

  • Blastocyst implants in the endometrium (now called decidua basalis).

  • Maternal veins and arteries bring blood into placental sinuses.

  • Chorionic villi extend into these sinuses.

  • Umbilical vein and arteries form capillary beds in the chorion.

  • Placental Barrier:

    • Separates maternal and fetal blood.

    • Formed by syncytiotrophoblast cells.

    • Allows exchange via diffusion (oxygen, nutrients from mom to baby; wastes from baby to mom).

  • Prevents mixing of blood.

Placental Functions

  • Transfer of nutrients, oxygen, and waste.

    • Oxygenated blood from maternal uterine arteries flows into sinuses.

    • Deoxygenated fetal blood flows through umbilical arteries to chorionic villi capillaries.

    • Waste is disposed of via maternal kidneys.

    • Exchange occurs via diffusion based on concentration gradients and affinity.

  • Endocrine function.

    • Produces hormones to maintain pregnancy.

    • Human chorionic gonadotropin (hCG).

    • Progesterone.

    • Estrogen.

Placenta Consumption

  • Animals eat the placenta for nutrition after giving birth.

  • Humans can obtain the same nutrients from other sources (e.g., hamburger).

  • No proven added benefits to eating the placenta in humans. Preparations include freezing, drying, and encapsulation.

Placental Issues

  • Placenta Previa:

    • Placenta attaches in the wrong place, often blocking the cervix.

    • Can cause rupture, hemorrhage, and infection.

    • Typically requires a cesarean delivery.

    • Amniotic fluid contains fetal urine and feces, increasing infection risk upon rupture.

Fetal Development: Month-by-Month

  • Maturation from head to butt, with significant weight gain in the last eight weeks.

  • Growth from 1 inch (embryo) to ~20 inches (fetus), with weight increasing by several pounds.

Month 3

  • Head growth slows.

  • Upper limbs reach birth length.

  • Ossification begins (bone development).

  • Eyes are developed, but on the sides of the head, eyelids are fused.

  • Bridge of the nose develops.

  • Ears develop, but are not prominent.

  • Genitals are distinguishable.

  • Size: ~3.5 inches.

Month 4

  • Rapid growth.

  • Lower limbs lengthen.

  • Joints form.

  • Skeleton continues to ossify.

  • Size: ~5.5 inches.

Month 5

  • Growth slows; limbs achieve correct proportions.

  • Hair growth on the head.

  • Skin covered in lanugo (downy hair) for protection.

  • Vernix caseosa (white, waxy coating) develops.

  • Brown fat forms for heat production.

  • Size: ~7.5 inches.

Month 6

  • Significant weight gain.

  • Eyebrows and eyelashes appear.

  • Eyelids partially open.

  • Skin is wrinkled and translucent.

  • Lungs begin to produce surfactant.

  • Size: ~9.1 inches.

Month 7

  • Eyelids are fully open.

  • Subcutaneous fat develops, reducing skin translucency.

  • Skin smoother but still wrinkled and red/pink.

  • Fetus is viable.

  • Size: ~11 inches.

Months 8-9

  • Neurons form networks (synaptic connections, memory).

  • Full term is considered 266 days.

  • Hair and fingernails are present.

  • Well-developed fingers and toes.

Fetal Circulation

  • Differs significantly from adult circulation due to the placenta.

  • Three shortcuts:

    • Foramen ovale: Bypasses the lungs.

    • Ductus arteriosus: Connects pulmonary trunk to aorta.

    • Ductus venosus: Bypasses the liver.

  • These shortcuts take about a year to fully close after birth. Heart murmurs can be associated with this process.

  • After birth:

    • Ductus arteriosus shuts quickly due to pressure changes from first breath, becomes the ligamentum arteriosum in about 3 months.

    • Ductus venosus degenerates to become the ligamentum venosum.

    • Umbilical arteries become the medial umbilical ligaments, and the umbilical vein becomes the round ligament of the liver.

Fetal vs Adult Circulation

  • Fetal venous system goes to the placenta before returning to the heart.

  • Foramen ovale: Connects the atria

  • Comparison of fetal structures to adult structures.

    • Formative bowel becomes the fossa of allus.

Premature Birth

  • Infant born more than three weeks before full term (38 weeks or 266 days).

  • About 12% of births are premature.

  • Earlier birth = greater risk.

  • Issues: Lack of fat deposits, temperature regulation problems, respiratory issues due to lack of surfactant.

  • May need ventilator support.

  • Reflexes for suckling and swallowing may not be developed.

  • Incubators help with thermoregulation.

  • Most common cause of infant death.

  • Survivors may face hearing loss, vision loss, cerebral palsy, learning disabilities.

Changes in Mom During Pregnancy and Childbirth

First Trimester (Months 1-3)

  • Fatigue, breast tenderness, mood swings.

  • Symptoms vary by individual.

Second Trimester (Months 4-6)

  • Fetus grows and develops.

  • Obvious signs of pregnancy (abdomen expands).

  • Lower risk of spontaneous abortion.

Third Trimester (Months 7-9)

  • Weight gain in fetus.

  • Uterus enlarges significantly.

  • Diaphragm compressed.

Uterus size changes

  • Non-pregnant: Fist size

  • First trimester

  • Second trimester.

  • Third trimester.

Hormonal Changes During Pregnancy

  • hCG maintains the corpus luteum.

  • Progesterone and relaxin suppress contractions and relax ligaments.

  • Placental lactogen stimulates mammary gland development.

  • Melanocyte-stimulating hormone changes pigmentation.

  • Corticotropin-releasing hormone influences the length of pregnancy.

Other Hormones

  • Increased aldosterone retains sodium and water.

  • Parathyroid hormone ensures adequate calcium levels.

  • Prolactin stimulates lactation.

Anatomical Changes in Mom

  • Uterus expands (size of a fist to filling the abdominal cavity).

  • Diaphragm is pushed upward, compressing lungs.

  • Backaches due to pressure on vertebrae.

  • Breasts are sore due to hormones.

Cardiovascular Changes

  • Blood volume increases.

  • Cardiac output increases.

  • Respiratory center becomes more sensitive to carbon dioxide.

  • Lungs cannot fully expand.

Digestive Changes

  • Pregnant woman needs about 300 extra calories.

  • Prenatal vitamins help meet nutritional needs.

  • Weight gain (average 28.7 lbs) is mostly water retention and amniotic fluid, and the weight of the fetus.. The food intake is usually much less than the water retention, etc.

  • Morning sickness, nausea, vomiting.

  • Hyperemesis gravid arum (severe morning sickness) dangerous due to dehydration and electrolyte imbalance.

  • Cravings, and aversions.

  • Progesterone relaxes smooth muscle, slowing peristalsis (constipation).

Urinary System Changes

  • Increased blood volume increases glomerular filtration rate.

Skin Changes

  • Increased pigmentation (melanocytes).

  • Chloasma (mask pattern) over eyes and cheekbones.

  • Striae (stretch marks) due to severing of elastic fibers.

  • Progesterone and estrogen decrease hair loss.

Pregnancy Complications

  • Preeclampsia:

    • 10% of pregnancies.

    • Unknown causes.

    • Symptoms: Increased blood pressure, protein in urine.

  • Eclampsia:

    • Escalation of preeclampsia, leading to seizures.

    • Very dangerous for mom and baby.

    • Delivery is the only treatment.

Childbirth (Parturition)

  • Process of expelling the fetus.

  • Baby's head pushes on cervix.

  • Mucus plug forms at the cervix during pregnancy.

Hormonal cascade and Feedback Loop

  • Cortisol stimulates the placenta to make estrogen.

  • Estrogen means the uterus forms oxytocin receptors, so now oxytocin can act on the uterus.

  • The hypothalamus of mom and baby make oxytocin, which stimulates the prostaglandins.

  • Prostaglandins dilate the cervix

  • Together with oxytocin, that will strengthen the uterine contractions.

  • More positive feedback: The more that baby pushes against that cervix, the more oxytocin, the more prostaglandins, and the more dilation and the more contraction seen.

Stages of Labor

  • Dilation: *The longest and most variable stage.

    • 8-24 hours.

    • Cervix dilates to 10 cm.

    • Amnion ruptures (water breaking).

    • Baby's head rotates and enters the true pelvis.

  • Expulsion:

    • From full dilation to delivery.

    • Vertex position (head first) is ideal. Issues with positioning can require a cesarean.

    • Shoulder dystocia can be life-threatening.

    • It can take a few hours.

  • Placental Stage:

    • After birth of the baby.

    • Delivery of the placenta and embryonic membranes.

    • Significant blood loss, major risk of infection is any part of the placenta stays in.