Conception & Fetal Development

What are dizygotic twins? What are monozygotic twins? WHat are multifetal pregnancies?

(Dizygotic) 2 Ova & 2 Sperm mix to make 2 Kids (Monozygotic) 1 Ova that is fertilized and divides (Multifetal Pregnancies) Triplets 149/100,000 births

What are the chances of having twins?

32 out of 1000 Births

What are teratogens? When is the embryo susceptible to damage?

A teratogen is a drug or other substance capable of interfering with the development of an embryo fetus that may lead to birth defects Developing embryo is highly sensitive to teratogens during weeks 3 to 9 of pregnancy

What is the significance of the Lecithin/Sphingomyelin Ratio?

Determines fetal lung maturity

What are normal amounts of amniotic fluid at 10 weeks and 36 weeks? What does amniotic volume tell you?

(Amount of fluid at 10 weeks) 30 ml at (Amount of fluid at 36 weeks) 500 ml to 1000 ml (Volume Tells You) Fetal well being < 300/500 ml at term: oligohydramniosis eg. assoc. renal abnormalities, IUGR, premature ROM > 2000 ml at term: polyhydramniosis, eg. assoc. GI abnormalities, CNS problems, genetic abnormalities, Rhesus isoimmunisation

What are the placental hormones and their function?

(Human Chorionic Gonadotropin, HCG) - Human chorionic gonadotropin is a hormone that is made by the corpus leutum and later by the PLACENTA. It interacts with the LHCG receptor and promotes the maintenance of the corpus luteum during the beginning of pregnancy, causing it to secrete the hormone progesterone. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus. (Human Placental Lactogen) -HPL decreases maternal insulin sensitivity, and, therefore, raises maternal blood glucose levels, whilst decreasing maternal glucose utilization, which helps ensure adequate fetal nutrition (Oestrogen) - Without estrogen, the lungs, kidneys, liver, adrenal glands and other organs would never be triggered into maturation. In fact, the placenta itself would never grow and operate properly if not for estrogen. (Progesterone) - Because progesterone helps to build the endometrial lining, it is important that its levels stay high in pregnancy. A thick lining is key for the healthy implantation of a fertilized egg. Low or dropping progesterone levels can be correlated with early miscarriage in pregnancy. High progesterone levels inhibit ovulation; (so a woman does not ovulate again after becoming pregnant until she is no longer pregnant.) Once a placenta develops in pregnancy, additional progesterone is produced from it. This progesterone helps to protect the placenta through fighting off unwanted cells that might harm the placenta or fetus. It strengthens the mucousal lining that covers the cervix; this protects infection from entering the cervix. Progesterone levels can inhibit the uterus from having contrations (which might play a role in terminating a pregnancy.) Relaxin - Softens and relaxes the pubic symphisis

Discuss the cycle of Estrogen and Progesterone as it pertains to onset of ovulation. What affect do these hormones have on the development and release of the egg?

(Video Review) http://www.youtube.com/watch?v=jbcnsA3FfgI&feature=related (Explanation) The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purposes of sexual reproduction and fertilization. This article focuses on the human menstrual cycle. The menstrual cycle, under the control of the endocrine system, is necessary for reproduction. It is commonly divided into three phases: the follicular phase, ovulation, and the luteal phase; although some sources use a different set of phases: menstruation, proliferative phase, and secretory phase.[1] Menstrual cycles are counted from the first day of menstrual bleeding. Hormonal contraception interferes with the normal hormonal changes with the aim of preventing reproduction. Stimulated by gradually increasing amounts of estrogen in the follicular phase, discharges of blood (menses) slow then stop, and the lining of the uterus thickens. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one or occasionally two become dominant (non-dominant follicles atrophy and die). Approximately mid-cycle, 24-36 hours after the Luteinizing Hormone (LH) surges, the dominant follicle releases an ovum, or egg in an event called ovulation. After ovulation, the egg only lives for 24 hours or less without fertilization while the remains of the dominant follicle in the ovary become a corpus luteum; this body has a primary function of producing large amounts of progesterone. Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will involute, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining and egg in a process termed menstruation.

Discuss fetal circulation. When does fetal heart start pumping? Does blood go to the fetal lungs? Why

(Video Review) http://www.youtube.com/watch?v=uwswhoKfkmM&feature=related *Fetal heart begins to pump by 3rd week Blood is shunted away from the lungs bc O2 is supplied by the placenta. The 2 shunts are: Foramen Ovale Ductus Arteriosis

When is a developing embryo considered a fetus? What development occurs during this time?

*9 weeks until the end of pregnancy During this time, the embryo becomes recognizable human. During the Maturation stage, refinement of structure & function is taking place

Discuss conception

1. 200 - 500 million spermatozoa deposited to external os of cervix during intercourse 2. Sperm remain viable for 2-3 days Within an hour of intercourse (!) 300 - 500 sperm have reached the ampullae 3. Most sperm die and are lost within cervical mucus, or enter the fallopian tube that has no ovum 4. As they travel, enzymes are produced to aid capacitation (this will enable them to penetrate the ovum before fertililization)

Discuss the umbilical cord formation

1. By day 14, the embryonic disk, amniotic sac & yolk sac are attached to the chorionic villi by the connecting stalk 2. During week 3, blood vessels develop to supply the embryo with maternal nutrients & 02 3. During week 5, embryo curves inward, connecting stalk becomes compressed by the amnion & forms the narrower umbilical cord 4. Two arteries and one vein

Briefly review the development of the fertilized ovum

1. Conception to14 days 2. Cellular replication, blastocyst formation, and the initial development of the embryonic membranes & establishment of primary germ layers

Discuss the importance of the yolk sac

1. Develops 8-9 days after conception 2. Forms primitive RBCs for first 6 weeks 3. Degenerates, incorporated into umbilical cord

Functions of Amniotic Fluid

1. Initially derived from maternal circulation 2. Maintains body temperature 3. Serves as oral fluid & waste repository 4. Cushions from trauma 5. Supports musculoskeletal development

What are the functions of the placenta?

1. Interface between mother & fetus 2. Produce hormones responsible for maternal-fetal exchange & maintenance of pregnancy 3. Protects fetus from maternal immune attacks 4. Maintains fetal metabolism

Discuss the embryonic phase and it's importance with regards to development

1. Occurs 15 days to 8 weeks 2. Most critical time in the development of the organ systems (Teratogens can really affect the development of the embryo at this point) 3. All organ systems & external structures are present @ end of 8 weeks

Discuss the development of the placenta

1. Precursor cells (trophoblasts) appear 4 days after fertilization 2. Structure complete by week 12, growth until week 20

Discuss the effects of progesterone

1. Secreted by corpus leutuem & later the Placenta 2. Highest levels in secretory phase 3. Decreases uterine motility/contractility 4. Prepares uterus for implantation 5. Stimulated further increase in blood supply to uterus 6. Stimulates production of thick cervical mucus 7. Stimulates breast tissue to increase in size and complexity 8. Temp rise of 0.3-0.6 deg C with ovulation and remains until menstruation

Discuss fetal lung maturity. How is the L/S determined?

1. Surfactant lines the fetal lungs & Lowers alveolar surface tension during extrauterine exhalation 2. Lecithin/sphingomyelin (L/S) ratio determines fetal maturity (L/S Ratios) Early in pregnancy, @ 20 Weeks L/S ratio = 0.5:1 30-32 weeks L/S ratio = 1:1 About 35 weeks L/S ratio = 2:1 *L/S ratio is determined by analysis of amniotic fluid through amniosentisis

Discuss the process of FERTILIZATION

1. Takes place in ampulla (outer 1/3 of fallopian tube) usually within 24 hours of intercourse 2. If not fertilised ....secondary oocyte degenerates and dies within 12 - 24 hours 3. Sperm remain alive for at least 24 hours (2-3 days) 4. Semen in vitro is viable for up to 4 days 5. Deep frozen (-79o to -196o) remains viable indefinitely 6. Results in restoration of the diploid number of chromosomes 7. Results in Species variation bc of a new combination of chromosomes 8. Gender determination X sperm will result in female; Y sperm will result in male (Video Review) http://www.youtube.com/watch?v=8ZL1ws-gaRg&feature=related (2nd Video) http://www.youtube.com/watch?v=_2MFFzldkYQ&feature=related

Discuss the role's of estrogen in the female body. Where does it come from?

1.Secreted by ovaries & placenta 2. Control development of secondary sex characteristics (breast development, fat deposits) 3. Assist in maturation of ovarian follicles 4. Stimulates proliferation of endometrial mucosa (preparation for implantation) 5. Associated with increasing blood supply to uterus

Discuss amniotic fluid composition

98% water + urea albumin fat fructose bilirubin epithelial cells

Discuss chorion and amnion

Both are membranes Chorion - Covers the fetal side of the placenta Amnion - Forms on the side opposite the developing blastocyst. This Sac surrounds/protects the embryo/fetus

When can WE HEAR the fetal heartbeat?

By 8th week of pregnancy via (Ultrasound Stethoscope)

Discuss the 3 primary germ layers and what they become

Ectoderm (upper layer of embryonic disk, epidermis, glands, nails, hair, CNS, PNS, optical lens, tooth enamel, floor of amniotic cavity) Mesoderm (Bones, teeth, muscles, heart, dermis, connective tissue) Endoderm (epithelium lining the respiratory tract & digestive tract, oropharynx, liver, pancreas, urethra, bladder & vagina)

During which part of the pregnancy is the developing offspring less vulnerable to teratogens?

Fetal Stage (9 Weeks to End of Pregnancy)

Summarize developmental benchmarks during pregnancy

Week 4 - Fetal heart beats Week 4 - Neural tube closes Week 5 - limb buds form Week 6 - genitals, fingers, primitive skeletal shape and inner ear develop, circulation established Week 7 - palate forming, foetal heartbeat detected, eyelids appear Week 9 - Kidneys function *All organ systems formed by 8-12 wks