NSG210 Week 03b Summary: OB Lecture 1 Continued - Genetics, Fetal Development, and Antepartal Testing
This fills the gap flagged in nsg210-week-03-summary and in the exam-1 study guide/tracker: the September 9, 2026 lecture (OB Lecture 1 on Canvas, syllabus Lectures 1-2, Durham Chapters 3-6) covers two distinct halves. The trends/ethics/legal/medications half is in nsg210-week-03-summary. This file covers the second half - genetics, conception, fetal development, teratogens, pregnancy physiology and psychosocial care, and antepartal testing - now that raw source material for it exists.
Note on naming: the source files for this content are raw/nsg210_wk03_LectureNotes.md, raw/nsg210_wk03_OBLecture1.md, and raw/nsg210_wk03_OBCh6.md. The “wk03” prefix matches the course week: September 9 is Week 03 on the Canvas layout, and this content is scoped to Exam 1, not Exam 2.
Genetics
Inheritance patterns: autosomal recessive (sickle cell anemia, cystic fibrosis, Tay-Sachs, PKU - both parents usually must carry the abnormal gene), autosomal dominant (Huntington’s disease - one affected parent can pass it to a child, often 50 percent risk), and X-linked recessive (hemophilia, Duchenne muscular dystrophy - primarily affects males, mother may be a carrier). Bottom-line pathway: family history leads to identifying the inheritance pattern leads to assessing risk leads to genetic counseling/testing leads to newborn screening.
Gametogenesis, Conception, and Fertilization
Oogenesis forms ova in the ovaries, begins before birth, and reduces chromosomes from 46 to 23. Spermatogenesis forms sperm in the testes, begins at puberty, also reduces 46 to 23, and determines fetal sex by contributing an X or Y chromosome. Conception follows ovulation (egg enters the fallopian tube) and ejaculation (sperm travels toward the fallopian tube); fertilization - egg (23) plus sperm (23) equals zygote (46) - usually occurs in the fallopian tube and marks the start of pregnancy.
Teratogens and Fetal Development
A teratogen is any substance, infection, or exposure that can harm the developing fetus. Drug/substance teratogens: alcohol (fetal alcohol spectrum disorders), ACE inhibitors (fetal kidney problems - also why ACE inhibitors are contraindicated in pregnancy, echoing the pharmacology point in nsg210-exam-1-studyguide), anticonvulsants (congenital abnormalities), cocaine (growth/placental problems), warfarin (fetal abnormalities and bleeding).
Infectious teratogens, largely the TORCH group: CMV (cytomegalovirus) is a herpesvirus and the leading infectious cause of congenital hearing loss - maternal infection is often mild or asymptomatic, but fetal transmission can also cause microcephaly, IUGR, hepatosplenomegaly, and developmental delay; it spreads through body fluids (saliva, urine, breast milk, sexual contact) with no widely used vaccine, so hand hygiene around young children is the main prevention. Other TORCH-type infections: varicella (fetal abnormalities), rubella (heart, eye, hearing problems), syphilis (fetal infection/pregnancy loss), toxoplasmosis (eye and brain problems), and Zika (microcephaly and brain abnormalities).
The embryonic period (weeks 3-8) is the most critical window for teratogen-related birth defects, since organogenesis is happening then. The pre-embryonic period (weeks 1-2) covers rapid zygote division, transport through the fallopian tube to the uterus, and implantation of the blastocyst into the uterine decidua (usually the upper uterine wall), which supports and nourishes the conceptus.
Fetal Growth Timeline and Circulation
Fetal development from weeks 9-38: 9-12 rapid growth and fetal movement begins; 13-16 facial features develop and sex may be identifiable; 17-20 quickening and lanugo; 21-24 lung development and response to sound; 25-28 improving viability, eyes open; 29-32 rapid brain/lung maturation and fat storage; 33-38 continued weight gain and organ maturation.
Fetal circulation runs through the umbilical cord (two arteries carrying deoxygenated blood, one vein carrying oxygenated blood) and three shunts that let blood bypass the non-functioning fetal lungs and liver: the ductus venosus, foramen ovale, and ductus arteriosus.
Multifetal Pregnancy and Infertility
Monozygotic (identical) twins come from one fertilized egg that splits into two embryos; dizygotic (fraternal) twins come from two eggs each fertilized by separate sperm. Three or more fetuses are higher-order multiples. Infertility causative factors split by sex: female (ovulatory dysfunction, tubal/pelvic pathology, cervical mucus factors) and male (endocrine, gonadotoxins, sperm antibodies, sperm transport, disorders of intercourse). Workup includes STI screening, semen analysis, and ovulatory/endometrial/radiological exams; treatment ranges from hormones and lifestyle changes to steroids, antibiotics, and surgery.
Signs of Pregnancy
Three tiers, increasingly specific: presumptive signs (amenorrhea, nausea/vomiting, fatigue, breast tenderness, urinary frequency, quickening) are what the woman reports and are not diagnostic since they can have other causes. Probable signs are provider-observed but still not proof: positive pregnancy test, enlarged uterus, Goodell sign (soft cervix), Hegar sign (soft lower uterine segment), Chadwick sign (bluish/purple cervix/vagina), and Braxton Hicks contractions (irregular, painless, no cervical dilation). Positive signs are proof of pregnancy because they come directly from the fetus: fetal heart rate heard by the provider, fetal movement felt by the examiner, and fetus visualized on ultrasound.
Physiologic Adaptations to Pregnancy
Cardiovascular: blood volume, heart rate, and cardiac output all increase to supply the uterus and placenta. Plasma volume rises more than RBC mass, producing physiologic anemia of pregnancy - Hgb/Hct may look low from hemodilution alone, not true anemia. Blood pressure may dip slightly in the second trimester.
Respiratory: oxygen consumption and tidal volume increase while respiratory rate stays about the same; mild dyspnea can be a normal finding, but severe or sudden respiratory distress is not.
GI: progesterone-driven smooth muscle relaxation slows GI motility, producing nausea/vomiting, heartburn/reflux, and constipation. Urinary: frequency is common in early and late pregnancy and can be normal; renal blood flow and GFR both increase. Reproductive/vaginal: the uterus enlarges, the cervix softens and becomes more vascular, and leukorrhea (thin, milky/white discharge) is normal - foul-smelling or green/yellow discharge, or discharge with itching/burning/bleeding/pain, needs assessment.
Skin: linea nigra, striae gravidarum, chloasma/melasma (“mask of pregnancy”), and areola darkening. Musculoskeletal: the center of gravity shifts forward, lordosis causes backache, and relaxin loosens pelvic ligaments to prepare for birth. Breast: enlargement/tenderness, areola darkening, prominent Montgomery glands, and colostrum (the antibody-rich first milk).
Dating and Assessing Pregnancy
Naegele’s rule for estimated date of delivery: LMP plus 7 days, minus 3 months, plus 1 year (“add 7, subtract 3, add 1”). Example: LMP June 10, 2026 leads to June 17 leads to March 17 leads to EDD March 17, 2027. Pregnancy runs about 40 weeks/280 days from the LMP: 1st trimester 0-13 weeks, 2nd trimester 14-27 weeks, 3rd trimester 28-40 weeks.
Fundal height in cm approximates gestational age in weeks after 20 weeks (20 weeks is roughly at the umbilicus; 24 weeks is roughly 24 cm). Smaller than expected suggests incorrect dates, growth restriction, or low amniotic fluid; larger than expected suggests incorrect dates, multiple pregnancy, or excess amniotic fluid. Measure with the woman supine, knees slightly flexed, symphysis pubis to fundus - expect normal variation, not an exact match.
GTPAL is a high-yield trap-heavy mnemonic: G = gravida (total pregnancies, current one included), T = term (births at 37 weeks or more), P = preterm (births from 20 weeks to 36 weeks 6 days), A = abortions (pregnancy loss before 20 weeks, spontaneous or induced), L = living (number of living children). Twins count as one pregnancy for G/T/P/A but two for L. The classic distractor: exactly 20 weeks counts as P, not A, since A requires before 20 weeks.
Differential vs. Definitive Diagnosis
A general diagnostic-reasoning concept that pairs with the screening-versus-diagnostic testing distinction below: differential diagnosis is the list of possible conditions that could explain the patient’s signs/symptoms, narrowed through history, exam, and testing. Definitive diagnosis is the single confirmed diagnosis, established once testing rules out the other possibilities on that list.
Antepartal Testing (Durham Chapter 6)
Testing during pregnancy checks maternal/fetal well-being, catches problems early, monitors fetal growth, and detects genetic/chromosomal abnormalities - especially for high-risk pregnancies (diabetes, hypertension/preeclampsia, prior pregnancy complications, decreased fetal movement, poor fetal growth, multiples, post-term, suspected fetal abnormality).
Screening versus diagnostic is the organizing distinction: screening tells you risk, doesn’t diagnose, and is usually less invasive (maternal serum screening, ultrasound, NST); diagnostic tells you whether a condition is present and can be invasive (CVS, amniocentesis, fetal blood sampling). This maps directly onto differential-versus-definitive diagnosis above.
Biophysical Profile (BPP) combines NST with ultrasound assessment of fetal breathing, movement, tone, and amniotic fluid - each of the 5 components scores 0 or 2, for a maximum of 10 (“baby’s 5 behaviors”). Ultrasound alone checks fetal growth, anatomy, position, placenta, amniotic fluid, and multiples - noninvasive, no ionizing radiation. Doppler flow assesses fetal/placental blood flow, placental insufficiency, and fetal growth problems.
Nonstress test (NST) watches fetal heart rate, movement, and accelerations. The reassuring pattern at 32 weeks or more is the memory aid 15-15-2: at least 2 accelerations of at least 15 bpm lasting at least 15 seconds, within a 20-minute window. Baby moves, heart rate goes up - that’s reassuring.
Diagnostic (biochemical) tests: CVS samples placental tissue for chromosomal/genetic abnormalities; amniocentesis samples amniotic fluid for genetic/chromosomal disorders and fetal maturity; PUBS samples fetal umbilical cord blood for blood disorders, infection, and genetic problems. Risks across these: miscarriage, bleeding/infection, amniotic fluid leakage, rare fetal injury - nursing actions are informed consent, maternal vital signs and FHR before/after, monitoring for complications, and Rho(D) immune globulin for an Rh-negative patient.
Maternal assays (blood-based screening): cell-free DNA (from 10 weeks, screens trisomy 21/18/13, can identify fetal sex, screening not diagnostic), alpha-fetoprotein/AFP (elevated suggests neural tube defect, low suggests Down syndrome), and multiple-marker screening (several markers together, screens chromosomal abnormalities and neural tube defects).
Antenatal fetal surveillance ties it together: fetal movement counting, NST, contraction stress test, amniotic fluid index, and BPP. The nurse’s role throughout antepartal testing is consistent regardless of which test: interpret reassuring versus abnormal results, know when to escalate, teach the patient, provide emotional support, and respect informed choice and privacy.