Week 1: Genetics, Conception & Fetal Development

Chromosomal Abnormalities include…

abnormal number, structure or sex chromosomes

Trisomy

extra chromosome

• ex: Trisomy 21 (Down Syndrome → can survive), Trisomy 18 (Edwards Syndrome → fatal in 1st year), Trisomy 13 (Patau Syndrome → fatal in few weeks)

Monosomy

single chromosome

• ex: Monosomy 45 (Turner Syndrome, single X) 

Mosaicism

Genetic condition where some cells have an abnormal number of chromosomes while others are normal

Common inheritance patterns include…

autosomal, dominant, autosomal recessive, x-linked recessive

Autosomal Dominant

sex doesn’t play a factor; only one copy of the altered gene is needed for expression (ex: Huntington’s Disease)

• 50% chance of passing on the gene

Autosomal Recessive

sex doesn’t play a factor; both parents must carry the defective gene (ex: cystic fibrosis

X-linked Recessive

abnormal gene on the X chromosome; affects males more often; no male to male transmission (ex: red-green color blindness)

Prenatal Genetic Testing: Screening Tests

Assess risk for genetic or chromosomal conditions but are not diagnostic; may require follow-up testing

Prenatal Genetic Testing: Diagnostic Tests

diagnose a condition; examines cells from fetus of placenta

Blood Test & PGT

type of prenatal genetic carrier screening test; can be performed pre-implantation

Blood Test: Cell-Free DNA Testing

screening test performed at 10+ weeks gestation that screens for chromosomal abnormalities such as Trisomy 21, 18, and 13; uses maternal blood

Ultrasound (Nuchal Translucency)

screening test performed at 10-13 weeks that measures length fetal neck to test for chromosomal abnormalities (ex: down syndrome)

Blood Test: Quad Screen

screening test performed at 15-22 weeks measuring AFP, hCG, unconjugated estriol, and inhibin-A to assess risk for neural tube or chromosomal defects

Ultrasound Scan

screening test performed at 18-22 weeks to look at the fetal anatomy

Chorionic Villus Sampling

diagnostic test performed at 10-13 weeks where placental tissue is removed to diagnose congenital abnormalities; amniotic sac not fully developed; can be performed transabdominally or trans cervically 

Amniocentesis

diagnostic test performed at 14+ weeks that collects amniotic fluid to assess for genetic or congenital disorders, fetal lung maturity, or infections; uses direct needle transabdominally into uterus

Menstrual Cycle: Menstrual Phase

1st stage; endometrial lining is shed (aka bleeding), progesterone + estrogen are low

Menstrual Cycle: Follicular Phase

2nd stage; occurs during days 1-13; pituitary releases FSH which stimulates egg maturation + thickening of uterine lining

Menstrual Cycle: Ovulation

3rd stage; occurs around day 14; increases LH causes egg to be released from ovary

Menstrual Cycle: Luteal Phase

4th stage; occurs around day 15-28; corpus luteum breaks down; progesterone + estrogen are low; next period starts 

Follicle Stimulating Hormone (FSH)

Secreted by the anterior pituitary; stimulates growth of ovarian follicles (aka egg maturation)

Luteinizing Hormone (LH)

Triggers ovulation and formation of the corpus luteum

Estrogen

Produced by the ovarian follicles; helps mature ovarian follicle and grow uterine lining

Progesterone

Secreted by the corpus luteum; levels increases during ovulation; maintains the uterine lining and relaxes uterine muscles during pregnancy (pregnancy hormone)

hCG

hormone produced after implantation; maintains corpus luteum until the placenta takes over progesterone production (~9 weeks)

Prostaglandins

produced by the endometrium (innermost lining of uterus); PGE relaxes smooth muscle, while PGF increases uterine contractility

Amnion

Inner membrane (second to ectoderm) that forms the amniotic sac and contains amniotic fluid; expands until it comes into contact w/ chorion

Chorion

Outermost membrane with chorionic villi; contributes to placenta formation

Fertilization

process by which egg becomes fertilized w/ sperm

• vagina → cervix (opens during ovulation) → uterus → ampulla of fallopian tube → egg

Implantation

occurs 6-10 days after fertilization; process by which blastocyte (divided zygote) attaches to the endometrium allowing for formation of placenta

Gastrulation

occurs around 3wk gestation; process by which embryo forms 3 germ layers (ectoderm, mesoderm, endoderm) that allow for development of all body systems 

Stages of Development: Embryonic Stage

Day 15 to 8 weeks; period of organogenesis and greatest vulnerability to teratogens

Stages of Development: Fetal Stage

Week 9 to birth; period of growth and functional maturation of organs

Which period is considered crucial period of development for fetus?

first 8 weeks then 16 weeks (CNS development)

Development Milestone: Week 8-12

FHR heard by doppler

Development Milestone: Week 16

baby’s sex visible on ultrasound

Development Milestone: Week 24

fetus is considered viable, activity increases

Monozygotic Twins

Identical twins from a single fertilized ovum that splits; same sex and genetic makeup; one placenta + two amnions + one chorion

Dizygotic Twins

Fraternal twins from two separate eggs and two sperm; genetically similar as siblings; two placentas + two amnions + two chorions

Amniotic Fluid (+amount)

fluid found in amniotic sac surrounding the fetus; increases w/ lung maturity

• composition: 98–99% water with albumin, urea, uric acid, creatinine, lecithin, and sphingomyelin

• function: cushions fetus, controls temperature, allows movement and growth, and protects umbilical cord

• amount: 30 mL (10 wk), 350 mL (20 wk), 800 mL (32-39 wk)

Oligohydramnios

Low amniotic fluid volume (<300 mL); associated with renal issues.

Polyhydramnios

Excessive amniotic fluid (>2000 mL); associated with GI or kidney malformations

Placenta

development occurs from wk 3-20 growing until covers ½ of uterus

• function: provides oxygen, nutrients, waste removal, hormone production (hCG, estrogen, progesterone), and passive immunity

Umbilical Cord Composition

Contains 2 arteries (carry deoxygenated blood to placenta) and 1 vein (carries oxygenated blood to fetus), protected by Wharton’s jelly (cushion)

Fetal Circulation

fetal lungs not involved in gas exchange requiring little blood; consists of 3 shunts: ductus venosis, ductus arteriosis, foramen ovale 

Ductus Venosis

helps oxygenated blood bypass the liver and enter the IVC to right atrium of fetal heart

Ductus Arteriosis

helps shunt deoxygenated blood from right ventricle to shunt to aorta of fetal heart

Foramen Ovale

opening that helps shunt blood from right to left atrium to help bypass lungs and oxygenate fetal organs

Teratogen

Substance that interferes with normal fetal development and causes congenital abnormalities; critical period from wk 3-8

Factors Influencing Embryonic & Fetal Development

quality of sperm or oocyte; adequacy of intrauterine environment; time of injury critical in development of anomalies, genetic code, maternal environment

Teratogens: FDA Drug Categories

• 8.1: Pregnancy (including L&D)

• 8.2: Lactation

• 8.3: Females and Males of Reproductive Potential

Nutrition During Pregnancy

helps prevent congenital malformations, recommended to make adaptations BEFORE pregnancy

• folic acid: essential for prevention of neural tube defects

Weight Gain + Nutritional Demands

should gain between 25-35lb depending on BMI; most weight gain occurs during 2nd and 3rd trimester; increase in blood volume 

• 1st trimester: no change

• 2nd trimester: increase 340kcal per day

• 3rd trimester: increase 452kcal per day

EDD Calculation

LMP - 3 months + 7 days

Quickening

fetal movement; felt at 16-20 weeks (if doesn’t take place after then want to investigate)

Fundal Height 

used to estimate fetal growth and gestational age during pregnancy

• 12-14 wk: just above the symphysis pubis

• 16 wk: halfway between symphysis pubis and umbilicus

• 20–22 wk: at the level of the umbilicus

• 36 weeks: reaches the xiphoid process of the sternum