OB Unit 3: Fetal Development & Changes During Pregnancy

where does fertilization occur?

the ampulla (outer third) of the fallopian tube during week 3 of the menstrual cycle (or within 12-24 hours post-ovulation)

what is the process of fertilization?

union of a single ovum and sperm forming a zygote containing 23 pairs (46 total) of chromosomes

how long are sperm and ova viable?

ova remain fertile for 12-24 hours post-ovulation; sperm remain viable in female reproductive tract for 3 days (72 hrs)

structure of placenta

formed from chorion (outermost membrane surrounding an embryo or fetus) and attached to the upper uterine wall; expelled post-delivery

functions of placenta

facilitates gas exchange, nutrient delivery, and waste removal between mother and fetus without direct blood mixing

metabolic activity of placenta

synthesizes glycogen and cholesterol for fetal energy and hormone production

endocrine function of placenta

produces essential pregnancy hormones including hCG, progesterone, estrogen, relaxin, and human placental lactogen (hPL)

vessel structure of umbilical cord

contains 1 umbilical vein and 2 umbilical arteries (in a “surprised face” arrangement) encased in protective Wharton’s jelly

umbilical vein function

transports oxygenated, nutrient-rich blood from the placenta to the fetal heart

umbilical arteries (2 of them) function

transports deoxygenated blood and metabolic waste from the fetus back to the placenta

ductus venosus (fetal circulatory shunt)

connects the umbilical vein directly to the fetus inferior vena cava, bypassing the immature fetal liver

foramen ovale (fetal circulatory shunt)

an opening between the right and left fetus atria that allows oxygenated blood to bypass the non-functioning fetal lungs

ductus arteriosus (fetal circulatory shunt)

connects the fetal pulmonary artery to the descending aorta, shunting blood away from the pulmonary circuit into systemic circulation

all 3 shunts close after birth due to increased oxygenation

primary function of amniotic fluid?

• protects the fetus from physical trauma

• cushions the umbilical cord against compression

• maintains stable fetal body temperature

• provides antibacterial protection

• allows symmetrical musculoskeletal growth

• supplies electrolytes/nutrients

derived from maternal serum; by week 10, fetal urine becomes the primary contributor

oligohydramnios

abnormally low amniotic fluid volume (associated with fetal anomalies or placental insufficiency)

polyhydraminos

abnormally high amniotic fluid volume (associated with GI tract obstructions or neural tube defects)

presumptive signs of pregnancy (subjective- felt by pt)

• amenorrhea

• fatigue

• nausea/vomiting

• breast tenderness/enlargement

• urinary frequency

• melasma

• quickening

probable signs of pregnancy (objective- assessed by provider)

• positive hCG pregnancy test

• Hegar’s sign (softening of lower uterine segment)

• Goodell’s sign (cervical softening)

• Chadwick’s sign (vioilet-blue discoloration of cervix/vagina)

• ballottement (examination method used to feel a solid object floating inside a fluid-filled part of the body)

• Braxton hicks contractions

• abdominal enlargement

• striae gravidarum

positive signs (diagnostic- attributed only to fetus)

• auscultation of fetal heartbeat

• fetal movement palpated by examiner

• direct visualization of the fetus/fetal cardiac activity on ultrasound

how do you calculate Estimated Date of Birth (EDB) using Naegele’s Rule?

Take the first day of the Last Menstrual Period, subtract by 3 months, add 7 days, and add 1 year

• ex: LMP= July 10, 2024 → - 3 months = April 10, 2024 → + 7 days = April 17, 2024 → + 1 year = April 17, 2025

Define each component of GTPAL

G (Gravida): Total number of pregnancies, including current pregnancy

T (Term births): number of births delivered at 37 weeks gestation or more

P (Preterm Births): Number of births delivered between 20-36 weeks gestation

A (Abortions): number of spontaneous, elective, or therapeutic losses prior to 20 weeks gestation

L (Living Children): total number of currently living children

hCG

earliest biochemical marker; maintains the corpus luteum to preserve early progesterone output until the placenta fully takes over

corpus luteum

secrete the hormone progesterone to prepare and maintain the uterus for a potential pregnancy (formed after mature follicle has been released)

progesterone

“hormone of pregnancy”; maintains the uterine wall lining, prevents smooth muscle uterine contractions, and supports vascular growth

estrogen

promotes uterine blood flow, maintains uterine lining, aids fetal organ maturation, and causes vascular/mucosal hypervascularity (nasal congestion/epistaxis)

relaxin

softens the cervix, relaxes pelvic ligaments/joints, and promotes uterine relaxation

oxytocin

stimulates uterine contractions during labor and initiates the milk-ejeciton reflex

what physiological changes occur in the cardiovascular and hematologic systems during pregnancy?

• volume & CO: blood volume expands by 30%-50% and CO increases by 30%-50%. Resting HR increases by 10-15 bpm

• anemia of pregnancy: due to hemodilution caused by volume expansion

• hypercoagulability

• supine hypotension syndrome: compression of the inferior vena cava by the uterus when lying flat, resolved by repositioning patient on left side

what physiological changes occur in the respiratory system?

• oxygen consumption increases

• thoracic chest diameter expands as the diaphragm is elevated upward

• estrogen-induced mucosal hyperemia causes “rhinitis of pregnancy” and nasal congestion

what physiological changes occur in the GI system?

• elevated progesterone relaxes smooth muscle reducing gastroesophageal sphincter tone and causing heartburn

• slowing intestinal motility (causing constipation)

what physiological changes occur in the renal system?

• GFR increases by 50%

• urinary frequency occurs in the the 1st trimester (due to hormonal/pelvic changes) and 3rd trimester (fetal head compression on bladder)

what physiological changes occur in the musculoskeletal system?

• shift in center of gravity induces lumbar lordosis (causes lower back pain)

• relaxin causes pelvic joint flexibility and a waddling gait

• diastasis recti (separation of rectus abdominis muscles)

what physiological changes occur in the integumentary system?

• linea nigra (dark midline abdominal pigmentation

• melasma/chloasma (mask of pregnanacy)

• striae gravidarum (stretch marks; persist permanently as silvery lines post birth)

what is the standard routine prenatal visit schedule for an uncomplicated pregnancy?

• initial vist by 10 weeks gestation

• conception to 28 weeks: visits monthly

• 28 weeks to 36 weeks: visits every 2 weeks

• 36 weeks to delivery: visits weekly

measurement method for measuring fundal height

measured in cm from top of the pubic symphysis to the top of the uterine fundus using a flexible tape measure

fundal height at 10-12 weeks gestation

fundus is palpable just above the symphysis pubis

fundal height at 16 weeks gestation

fundus is halfway between the symphysis pubis and umbilicus

fundal height at 20 weeks gestation

fundus reaches umbilicus (20 cm)

fundal height at 36 weeks gestation

fundus reaches just below the xiphoid process

first trimester expected manifestations

• fatigue

• morning sickness

• breast tenderness/fullness

• urinary frequency

• leukorrhea (increased vaginal discharge

• nasal stuffiness

first trimester warning signs

• severe abdominal cramping and/or vaginal bleeding: may indicate spontaneous abortion

• dysuria: indicates UTI

• severe, persistent vomiting: indicates hyperemesis gravidarum

• fever & chills: may indicate systemic infection

what are the psychological phases of maternal acceptance of pregancy?

• first trimester (ambivalence): conflicting feelings about pregnancy are a normal expected response, even if planned. Patient focuses on concept: “I am pregnant”

• second trimester (acceptance & quickening): perception of fetal movement (quickening at 16-20 weeks) fosters emotional attachment. Patient focuses on: “I am going to have a baby”

• third trimester (preparation): narcissism/inroversion, nest-building behaviors, and preparing for birth. The patient focuses on: “I am going to be a mother”

when is the fetus most vulnerable to teratogens?

the embryonic period (weeks 3-10 gestation) due to rapid organogenesis

what are the risks of tobacco/smoking on fetus?

• fetal vasoconstriction

• placental abruption

• intrauterine growth restriction

• low birth weight

• preterm birth

• sudden unexpected infant death

what are the risks of alcohol on fetus?

passes the placenta within menutes (fetal blood alcohol level = maternal blood alcohol level)

• causes fetal alcohol syndrome

• microcephaly

• facial dysmorphology

• cognitive impairment

• spontaneous abortion

what is the recommended total weight gain during pregnancy based on pre-pregnancy BMI?

• Underweight (BMI < 18.5): 28 to 40 lbs

• normal weight (BMI 18.5-24.9): 25 to 35 lbs

• overweight (BMI 25-29.9): 15 to 25 lbs

• obese (BMI > 30): 11 to 20 lbs

what are the key maternal nutritional guidelines?

• folic acid: 400-800 mcg daily 3 months preconcetion and during pregnanccy to prevent neural tube defects

  • dark leady vegetable, beans, fortified cereals, orange juice

• iron supplementation: supports expanded red cell volume; take with vit C to enhance absorption; avoid with milk/calcium or antacids

vegetarian/vegan diet guidelines

requiers direct supplementation of Vitamin B12, as well as monitoring calcium, vit D, and zinc levels

unsafe/foods to avoid during pregnancy

• high-mercury fish

• raw/undercooked meat

• raw seafood/sushi

• unpasterurized dairy or soft cheeses

• unheated deli meats

• raw sprouts

• raw eggs