Beginning of 3 rd month to end of pregnancy Fetal period
Supportive Structures Certain structures develop to support, maintain, new life throughout pregnancy – Embryonic or fetal membrane (chorion and amnion) – Placenta – Umbilical cord
Amnion Envelop the embryo and umbilical cord.
Lifeline between placenta and fetus Contains 3 vessels – 2 umbilical arteries – 1umbilical vein Wharton’s jelly – Gelatinous material surrounding cord – Prevents cord from collapsing, kinking inches long
8th week 30 mm amniotic sac umbilical cord placenta
Amniotic fluid Amniotic fluid contains – Fetal urine – Fetal hair – Sabaceous materials – Epithelial cells – Clear fluid /98% water Functions – Prevents amnion from sticking to embryo – Allows movement of embryo – Maintains constant normal body temp. for embryo – Helps to protect fetus from outside injury – Provides nourishment (can drink up to … daily) Amniotic fluid initially is isotonic, but as fetus develops; concentration changes by urine and sloughed cells of the fetus, placenta, and amniotic sac.
– Contains ml of amniotic fluid – Oligohydramnios: < 500 ml Causes associated with oligohydramios – Fetal genitourinary anomalies – Uteroplacental insufficiency – Fetal hypoxia – Polyhydramnios: > 2000ml at birth Factors associated with polyhydramnios – Spinal bifida – Anencephaly – Diabetes Amniotic sac at term
What is a placenta? Temporary structure Functions as an organ and endocrine gland Is shared by embryo and the woman Fully functional by the 12 th week of pregnancy
The Fetus Week 16 The Fetus Week 8
How is the placenta formed? – Outermost layer of “bag of waters” is chorion – Finger-like projections from chorion form chorionic villi – Chorionic villi embed within the decidua forming the placenta
Placenta Syncytiotrophoblast secretes enzymes that create blood filled cavities in the maternal tissue. Cytotrophoblast then forms villi that grow into the pools of venous blood. – Produces chorion frondosum on the side that faces the uterine wall. Other side of chorion bulges into the uterine cavity(chorion laeve).
Placenta Decidual reaction: – Endometrial growth. – Accumulation of glycogen. Decidua basalis: – Maternal tissue in contact with the chorion frondosum. Decidua basalis and chorion fondosum together become placenta.
Circulation is the result of a decidual reaction – Stromal cells of the endometrium enlarge – Capillaries become dilated and form sinusoids – Erosion of these sinusoids by the trophoblast fills area with maternal blood establishing a primitive circulatory system Maternal circulation in the placenta is outside of the maternal circulator system
Placental circulation Maternal blood flows into spaces between villi (intervillous spaces) Returns fetal waste products to maternal circulation Maternal and fetal blood does not mix unless there is a rupture of the chorionic villus
Size & shape of placenta Fetal surface Maternal surface
Placenta Function – Transfer of oxygen and nutrients to fetus – Removes fetal waste – Protects fetus by transferring maternal antibodies to fetus Synthesis of hormones to maintain pregnancy (endocrine gland) – Estrogen – Progesterone – Human chorionic gonadotropin (HCG) – Human placental lactogen(HPL) – Relaxin
Progesterone – Aids in development of the decidua – Progesterone Decreases uterine contractility – Promotes fat storage to prevent starvation – Decreases GI motility and bladder/ureter toneStimulates uterine growth. – Suppresses LH and FSH. – Stimulates development of alveolar tissue of the mammary gland. Estrogen Promotes growth and enlargement of fetus Endometrial growth. Promotes maternal vascularity stimulates ductal development in breast Causes pigmentation changes Inhibition of prolactin secretion. Enlargement of mother’s uterus. Placental hormones
HCG – Stimulates the corpus luteum to release estrogen/progesterone until placenta is functional Stimulates male fetus to release testosterone /aids in intrauterine development of male reproductive tract – Responsible for positive home pregnancy test – Prevents immunological rejection of implanting embryo. – Has thyroid-stimulating ability. – Produces effects similar to LH. HPL (human placental lactogen) Promotes maternal changes in metabolism (increased to meet needs of growing fetus) Contributes to breast enlargement Relaxin Promotes relaxation of sacroiliac, sacroccygeal, and pubic joints Prevents premature labor contractions Promotes cervical softening Placental hormones
crown-rump length (CRL) (sitting height) crown-heel length (CHL), the measurement from the vertex of the skull to the heel (standing height)
Length(3,4,5 months) Weigh 5 month= 500 gr. Weight(8,9 months),3600 gr.
In general, the length of pregnancy is considered to be: 266 days or 38 weeks after fertilization 280 days, or 40 weeks after the onset of the last normal menstrual period(LNMP)
50 mm 9 weeks Toes separate eyelids develop major parts of brain are present
61 mm 10 weeks Chin grows nostrils separate face appears human genitals appear male or female
11 weeks Well-defined neck appearing genitalia are completing sucking reflex appearing 73 mm
87 mm 12 weeks Well-defined neck appears Fingers/toes formed Nail beds begin formation Tooth buds present Placenta totally formed and functioning FHT audible with doppler
12 weeks sucking reflex appears Genitalia are complete
3 rd Month Position of eyes and ears Position of limbs Primary ossification centers Return of physiological hernia Sex definition Nervous reflexes
140 mm 16 weeks all major organs form Blood cells form Palate and nasal septum closure Swallows amniotic fluid and excretes urine Head hair & Lanugo(body hair ) forms over body movements are felt by mother
20 weeks Quickening (fetal movement) by primipara Considered the age of viability because some infants have survived at this age
5 th Month Lanugo hair on body Hair of head and eyebrows Sense of fetus movement by mother
230 mm 24 weeks Skin is wrinkled fat depositing under skin(Subcutaneous fat ) Eyebrows and eye lashes are formed pupils react to light Lung alveoli maturation & lung circulation develop
270 mm 28 weeks Fetus may be viable if born eyelids open Vernix caseosa protects skin
6 th, 7 th Month 25 Cm, 1100 gr. Red and shrink skin
300 mm 32 weeks most senses are well developed fat deposits increase body hair is lost but head hair is well developed Fingerprint formation Areola of breast visible but flat Skin is pink Vigorous fetal movement
36 weeks Lanugo is disappearing Breast tissue further develops Body begins to look plump and rounded fetus turning head down in uterus
350 mm 40 weeks Infant is full-term Skin is smooth; lanugo is gone from face and extremties Fingernails are fully formed and extend to ends of fingers Eye color is established Head erect
8 th, 9 th Month Vernix caseosa 3600 gr. CRH=36 Cm CHL=50 Cm
IUGR Intrauterine Growth Restriction SGA Small for Gestational Age Fetally Malnourished Dysmature
IUGR 10% With: neurological deficiencies congenital malformations meconium aspiration Hypoglycemia Hypocalcemi Respiratory distress syndrome (RDS). higher in blacks than in whites
Causative factors : chromosomal abnormalities (10%) teratogens congenital infections (rubella, cytomegalovirus, toxoplasmosis, and syphilis) poor maternal health (hypertension and renal and cardiac disease the mother’s nutritional status and socioeconomic level; her use of cigarettes, alcohol, and other drugs placental insufficiency; and multiple births (e.g., twins, triplets
The major growth-promoting factor during development before and after birth is insulinlike growth factor-I (IGF-I), which has mitogenic and anabolic effects. Fetal tissues express IGF-I and serum levels are correlated with fetal growth. Mutations in the IGF-I gene result in IUGR and this growth retardation is continued after birth.
In contrast to the prenatal period, postnatal growth depends upon growth hormone (GH). This hormone binds to its receptor (GHR), activating a signal transduction pathway and resulting in synthesis and secretion of IGF-I. Mutations in the GHR result in Laron dwarfism, which is characterized by growth retardation, midfacial hypoplasia, blue sclera, and limited elbow extension. These individuals show little or no IUGR, since IGF-I production does not depend upon GH during fetal development.