Conception and Fetal Development, Genetics

10 questions

fetal development wk 4

• beginning development of GI tract 

• Heart is developing 

• Somites develop → beginning vertebrae 

• Heart is beating and circulating blood 

• eyes and nose begin to form

• arm and leg buds are present

fetal development wk 6`

• trachea is developed

• liver produces blood cells

• trunk is straighter

• digits develop

• tail begins to recede

fetal development wk 12

• eyelids are closed 

• tooth buds appear 

• fetal heart tones can be heard 

• genitals are well-differentiated 

• urine is produced 

• spontaneous movement occurs 

fetal development wk 16 

• lanugo (baby hair) begins to develop 

• blood vessels are clearly developed 

• active movements are present

• fetus makes sucking motions 

• swallows amniotic fluid 

• produces meconium 

fetal development wk 20

• subQ brown fat appears

• **quickening is felt by mother (baby starts moving)**

• nipples appear over mammary glands

• fetal heartbeat is heard by fetoscope

fetal development wk 24

• eyes are structurally complete (should be able to open eyes)

• vernix caseosa covers skin

• alveoli are beginning to form

fetal development wk 28

• testes begin to descend 

• LUNGS ARE STRUCTURALLY MATURE (not functionally mature) → if baby is preterm, delaying to 28 weeks can improve prognosis

fetal development wk 32

• rhythmic breathing movements (breathe in and out amniotic fluid)

• ability to partially control temp

• bones are fully developed but soft and flexible

fetal development wk 36

• inc in subQ fat → biggest WEIGHT GAIN last few wks of gestation

• lanugo (baby hair) begins to disappear

fetal development wk 38

• skin appears polished

• lanugo has disappeared except in upper arms and shoulders

• hair is now coarse and ~1inch in length

• fetus is flexed

factors influencing development 

• quality of sperm or ovum (inc age = dec quality) 

• genetic code

• adequacy of intrauterine environment (Mom getting adequate nutrients) 

• teratogens 

  • high pollution (air/water pollution linked to preterm birth)

  • occupational hazards

  • meds

geriatric Mom/Dad age

• geriatric Mom at 35 y/o 

• geriatric Dad at 50 y/o 

ovarian cycle

• Follicular phase (days 1-14) 

• Graffian follicle appears by day 14

• Luteal phase (days 14-28)

• begins on 1st day of bleeding

• day 12 → lots of estrogen → pituitary gland releases LH

ovulation 

release of ripe egg 

menstrual cycle

• Menstrual phase = endometrium sheds 

• Proliferative phase (growing) = endo-and myometrium thickens; estrogen levels peak right before ovulation

• Secretory phase = progesterone dominate; estrogen drops sharply; uterus ready for implantation 

• Ischemic phase = estrogen and progesterone levels fall; vasoconstriction of uterine arterioles (think ischemic = less blood b/c of vasoconstriction) 

GnRH

causes anterior pituitary to release FSH and LH

FSH

maturation of follicle 

LH

release of mature follicle

estrogen

assists in maturation of ovarian follicles

progesterone 

prepares the uterus for implantation and prepares the breasts for lactation 

cervix

“door” to uterus

• internal os and external os = doors; sometimes 1 is open and 1 is not

• function:

  • lubrication of vagina

  • acts as bacteriostatic agent

  • provides an alkaline environment

uterine corpus

body of uterus

• perimetrium = peritoneum

• myometrium = muscle layer

• endometrium = mucosal layer

  • sheds in menstrual cycle

fallopian tubes

• transport of the ovum to the uterus

• site for fertilization

• nourishing environment for ovum/zygote

ovaries

• store and develop follicles

• secrete hormones → estrogen and progesterone

male external genitals

penis and scrotum

male internal reproductive organs 

• testes 

• epididymis

• vas deferens → gets cut / clamped in vasectomy 

• ejaculatory ducts 

• urethra 

• accessory glands 

epididymis

stores sperm for 2-10 days

mitosis

exact copies of original cell

meiosis 

production of new organism

• 1st division = mitosis

• 2nd division = chromatids separate and move to opposite poles → cells divide, forming 4 daughter cells

• end up with haploid cells (half genetic material) 

oogenesis

• ovary gives rise to oogonial cells → cells develop into oocytes

• meiosis begins and stops before birth

• cell division resumes at PUBERTY → development of Graafian follicle (mature follicle)

spermatogenesis

• production of sperm

• 1st meiotic division = primary spermatocyte replicates and divides

• 2nd meiotic division = secondary spermatocytes replicate and divide

• produce 4 spermatids

fertilization

• sperm and ovum unit to form zygote

  • sperm must pass through cervix (open while ovulating) to uterus

  • one fallopian tube empty; one contains egg

  • sperm binds to sperm receptors on egg

  • zona pellucida hardens after fertilization → prevents more sperm from entering

  • secondary oocyte completes second meiotic division → forms nucleus of ovum → nuclei of ovum and sperm unite → membranes disappear → chromosomes pair up

• ova are fertile for 12-24hr

• sperm are fertile for 72hr

• takes place in ampulla of fallopian tube

autosomal dominant disorders 

• Multigenerational 

• 50% change of passing on gene 

• Males and females EQUALLY affected 

• Varying degrees of presentation 

• Ex: Huntington’s, Achondroplasia (dwarfism) 

autosomal recessive disorders

• Carrier parents 

• 25% chance of passing on abnormal gene 

• 25% chance of an affected child 

• If a child is clinically normal, 50% chance child is carrier 

• Males and females EQUALLY affected 

• Ex: sickle cell, cystic fibrosis, Tay-Sachs 

X-linked recessive disorders

• NO male-to-male transmission 

• MORE COMMON IN MALES 

• 50% chance carrier mother will pass the abnormal gene to sons → affected

• 50% chance carrier mother will pass abnormal gene to daughters → carrier 

• Ex: hemophilia, DMD

implantation

• occurs 7-10 days after fertilization

• blastocyst burrows into endometrium

• endometrium now called decidua

placenta 

• metabolic and nutrient exchange

• maternal portion = decidua

• fetal portion = chorionic villi (shiny, whitish blue)

• fetal surface covered by amnion (bag of water)

placental functions

nutrition, excretion, fetal respiration , production of fetal nutrients and hormones

umbilical cord 

• body stalk fuses with embryonic portion of the placenta

• provides circulatory pathway from chorionic villi to embryo 

  • ONE VEIN = delivers oxygenated blood to fetus

  • TWO ARTERIES = carry waste products away from fetus to placenta

indications for preconceptual genetic testing

1. Geriatric pregnancy = Maternal age 35+

2. Family hx 

   1. Known or suspected Mendelian genetic disorder 

   2. Birth defects and/or mental retardation 

3. Previous pregnancies 

   1. Previous child with chromosomal anomaly 

   2. Previous child with metabolic disorder 

   3. 2 or more first trimester spontaneous abortions 

4. Parental genetics 

   1. Couples with a balanced translocation 

   2. Couples who are carriers for a metabolic disorder 

5. Abnormal MSAFP (Maternal Serum Alpha-Fetoprotein) 

   1. Screening for birth defects 

6. Women with teratogenic risk 

genetic testing — options that are JUST screening 

1. Sequential (10-13 wks) 

   • Nuchal translucency 

   • PAPP-A and hCG 

2. MSAFP quad screen (15-21 wks) = NOT diagnostic, just inc r/o 

   • AFP, inhibin, Estriol, hCG

   • Free cell DNA (at 10 wks) 

3. 20 wk ultrasound (18-22wks) 

genetic testing — actual test / determination

1. Genetic amniocentesis (15-18wks)  = tap and sample amniotic fluid; past deadline for TAB 

2. Chorionic villus sampling (10-13wks) = riskier (inc r/o SAB) 

Nurse’s role in genetic counseling

1. Educate about tests 

2. Provide support 

3. Refer for counseling 

4. Resource during and after counseling

Down syndrome

trisomy 21 = extra copy of chromosome 21

what wk of gestation is quickening felt by mother?

wk 20

what week of gestation are alveoli beginning to form?

wk 24

what week of gestation are lungs structurally mature (but not functionally)?

wk 28 → delaying premies to 28 wks GREATLY increases prognosis 

what week gestation does largest weight gain begin?

wk 36