+ Chapter 12 Conception and Fetal Development Maternity & Women’s Health Care, 11 th Edition by Lowdermilk, Perry, Cashion, and Alden Instructor: LaTricia Perry, MSN, RN, COI

+ Learning Objectives Summarize the process of fertilization. Identify growth and development of the embryo/fetus. Differentiate conception age from gestational age. Describe functions of components of conception: amniotic sac, placenta, umbilical cord. Describe placental and fetal circulation. Recognize periods of susceptibility to teratogens.

Conception: a sequential process Gamete formation OvulationFertilization Implantation in the Uterus

+ Cell Division Review The replication of a body cell to yield two cells identical to the parent cell. This type of cell division facilitates growth and development or cell replacement. Germ cell division resulting in half the original chromosomal number (23 single each). Produces gametes---sperm and ovum. Mitosis Meiosis- Gametogenesis

+ Gametogenesis and Fertilization

+ Duration of Pregnancy Conception Age Starts when the egg is fertilized by the sperm. Conception occurs approx. 2 weeks after the first day of the last menstrual period (LMP) Total of 266 days or 38 weeks Used in the discussion of fetal development Gestational Age Starts the from the first day of the LMP Used to mark the pregnancy time of 40 weeks, 10 lunar months, 9 calendar months, or 280 days.

+ Follicular Development and Implantation

+ Development of the Embryo Embryonic DiskEctoderm Epidermis; glands; nails and hair; CNS and PNS; lens of the eye; tooth enamel; the floor of the amniotic cavity Mesoderm Bones and teeth; muscles; the dermis and connective tissue; the cardiovascular system and spleen; the urogenital system Endoderm AKA Entoderm Epithelium lining of the respiratory and digestive tracts and the glandular cells assoc. with organs; the liver and pancreas; the urethra; the bladder; the vagina; and forms the roof of the yolk sac

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+ Formation of Membranes Chorion Develops from trophoblasts Contains chorionic villi that will eventually atrophy to create a smooth surface. Becomes the covering of the fetal side of the placenta Contains the major umbilical blood vessels Amnion Develops from interior cells of blastocyte Becomes the covering of the umbilical cord and covers the chorion on the fetal surface of the placenta. As the embryo grows larger, the amnion enlarges to accommodate the embryo/fetus and the surrounding amniotic fluid.

+ Amniotic Fluid Derives its fluid by diffusion from maternal blood as well as fluids secreted by the respiratory and GI tracts of the fetus. Serves many functions: Maintains constant body temperature Source of oral fluid and repository for waste Maintains fluid and electrolyte homeostasis Allows freedom of movement for musculoskeletal development Cushions fetus from trauma by blunting or dispersing outside force Acts as a barrier to infection Allows fetal lung development Keeps the embryo from tangling with the membranes Fetal well-being can be assessed by evaluating fluid volume

+ Yolk Sac A blastocyte cavity that develops on the other side of the developing embryonic disk. Aids in transferring maternal nutrients and oxygen to the embryo. Manufactures blood cells and plasma. Becomes the primitive digestive system for the embryo.

+ Umbilical Cord Development The connecting stalk on the ventral side of the fetus, becomes compressed from both sides by the amnion to form the narrower umbilical cord. Within the umbilical cord: Two arteries carry blood from the embryo to the chorionic villi. One vein returns blood to the embryo. Cord is 2cm in diameter and ranges from 30 to 90 cm long at term. Wharton’s jelly (connective tissue) is present to prevent compression and to ensure continued nourishment of the embryo/fetus. Usually located centrally on the placenta

+ Placental Structure Maternal (or uterine) surface Fetal (or amniotic) surface Amnion and smooth chorion are fused and continuous with margins of placenta

+ Placental Structure (cont) Circulation in place by day 17. By week 3, embryonic blood is circulating b/w embryo and chorionic villi. Maternal blood supplies oxygen and nutrients to the embryonic capillaries in the villi. Waste products and carbon dioxide diffuse into the maternal blood.

+ Placental Function Acts as an endocrine gland to produce various hormones Human chorionic gonadotropin (hCG) Human chorionic somatomamotropin (hCS) Progesterone Maternal Estrogens Metabolic Functions Respiration Nutrition Excretion Storage

+ Fetal Maturation Fetal Circulatory System

+ Fetal Maturation Hematopoietic System Formation of Blood Begins in 3 rd week Antigenic factors that determine blood type are present after the 6 th week. GI System Yolk sac becomes the primitive gut Foregut, midgut, hindgut Gastric emptying and intestinal peristalsis occur by the 5 th month. Meconium System mature by 36 weeks. Hepatic System Liver and biliary tract develop from the foregut during the 4 th week of gestation. Glycogen stores Iron Stores Hyperbilirubinemia Vitamin K Respiratory System Development begins during embryonic life and continues through fetal life and into childhood. Pulmonary Surfactants Fetal respiratory movements Fluid remaining in lungs at birth

+ Fetal Maturation (cont) Renal System Kidneys form during 5 th week and function approx. 4 weeks later. Renal malformations are diagnosable in utero. Kidneys are fully developed by term. Newborns should void within 24 hours of birth. Neurological System Originates from the ectoderm. Brainwaves are detectable by week 8. Movements detectable by mother by wk Sensory Awareness At term, the fetal brain is approx. ¼ the size of an adult brain. Endocrine System Thyroid gland develops by 3 rd -4 th week. Congenital hypothyroidism Adrenal cortex is formed during 6 th week and produces hormones by 8 th or 9 th week. Pancreas forms during the 5 th -8 th weeks with insulin production by week 20. Musculoskeletal System Bones and muscules develop by 4 th week. Ossification continues throughout childhood. Fontanels

+ Fetal Maturation (cont) Reproductive System Sex differentiation begins in the 7 th week. Distinguishing characteristics appear around the 9 th week and are fully distinguishable by 12 th week. Pseudomenstruation “Witch’s milk” Integumentary System Vernix caseosa At 17 weeks, skin is think and wrinkled with blood vessels visible underneath. Subcutaneous fat is present at 32 weeks. Lanugo appears first at 12 weeks on the eyebrows and upper lip. Covers the entire body by 20 weeks. Fingernails/toenails Immunologic System During 3 rd trimester, albumin and globulin are present. IgG crosses the placenta providing passive immunity. The fetus produces IgM by the end of the first trimester. Colostrum contains large amounts of IgA which is not produced by the fetus allowing for passive immunity. The preterm infant is at much greater risk for infection thank a term infant.

+ Multifetal Pregnancy Twins Dizygotic Monozygotic Conjoined

+ Factors Influencing Development Genetics Maternal Malnutrition Teratogens

+ Questions, Comments or Concerns???