2009 Lecture 23
Birth and Postnatal Development
There are a great number of comprehensive, scientific and general, books and articles that cover Parturition, Birth or Childbirth.
Birth or parturition is a critical stage in development, representing in mammals a transition from direct maternal support of fetal development, physical expulsion and establishment of the newborns own respiratory, circulatory and digestive systems.
- Human Embryology (2nd ed.) Larson Chapter 15 p471-488
- The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 7 p129-167
The median duration of gestation for first births from assumed ovulation to delivery was 274 days (just over 39 weeks). For multiple births, the median duration of pregnancy was 269 days (38.4 weeks).
- "...one should count back 3 months from the first day of the last menses, then add 15 days for primiparas or 10 days for multiparas, instead of using the common algorithm for Naegele's rule." Reference: Mittendorf R, Williams MA, Berkey CS, Cotter PF. The length of uncomplicated human gestation. Obstet Gynecol. 1990 Jun;75(6):929-32
Historically, Franz Carl Naegele (1777-1851) developed the first scientific rule for estimating length of a pregnany.
- Parturition (Latin, parturitio = "childbirth") describes expelling the fetus, placenta and fetal membranes and is probably initiated by fetus not mother.
- Preterm birth - Risks of preterm birth in abnormal low birth weight (intrauterine growth restriction) and high (large for gestational age) categories are 2- to 3-fold greater than the risk among appropriate-for-gestational-age infants.
- Maternal labor - uterine contractions and dilation of cervix, process under endocrine regulation
- Placenta and fetal membranes - (Latin, secundina = "following") expelled after neonate birth
Uterine Myometrial Changes
- Smooth muscle fibers - hypertrophy not proliferation
- Stretching of myometrium - stimulates spontaneous muscular contraction, during pregnancy progesterone inhibits contraction
- Stimulating contraction - increased estrogen levels (placental secretion sensitizes smooth muscle), increased oxytocin levels (fetal oxytocin release- force and frequency of contraction), fetal pituitary prostaglandin production (estrogen and oxytocin stimulate endometrial production of prostaglandin)
- maintains pregnancy - initially synthesized by corpus luteum, then levels maintained by placenta
- hyperpolarizes myometrial cells (-65 mV), reduces excitability and conductivity
- Level in plasma may fall just before parturition, definitely decreases following delivery of placenta
- Group of steroidal hormones, peak when parturition begins
- induce increased synthesis of actomyosin and ATP in myometrial cells
- alter membrane potential (-50 Mv) enhances excitation/conduction
- act to directly increase myometrial contraction
- indirectly by increasing oxytocin from pituitary gland
- Estriol - synthesized by fetus and placenta
- Peptide hormone (8aa) from maternal posterior pituitary, initiation and maintenance of labour (synthetic form labour induction)
- myometrium sensitivity to oxytocin (increased by estrogen, decreased by progesterone)
- stimulus for release - mechanical stimulation of uterus, cervix and vagina (ethanol inhibits release)
- hydroxy fatty acids - sythesized by placenta, amniotic fliud contains mainly PGF2 alpha, causes myometrial contraction (also in maternal plasma)
- PGF2 alpha and PGE2 - used to induce labour (intravenous, oral, intravaginal, intraamniotic)
- Aspirin inhibitor of PG synthesis - leads to increased duration of pregnancy
- mainly shown in other species parturition occurs in peaceful undisturbed surroundings, stress may have an inhibitory effect on oxytocin release
- Most human births occur at night (peak at 3am) diurnal rhythm influence
Stage 1 - dilatation
- uterine contractions 10 minutes apart, function to dilate cervix fetal membranes rupture releasing amnion, 7 -12 hours (longer for first child)
Stage 2 - expulsion
- uterine contractions push fetus through cervix and vagina, contractions 2-3 minutes apart, 20 - 50 minutes
Stage 3 - placental
- following child delivery contractions continue to expel placenta. haematoma separates placenta from uterine wall, separation occurs at spongy layer of decidua basalis, 15 minutes
Stage 4 - recovery
- continued myometrial contraction closes spiral arteries, 2+ hours
Newborn has to establish new functioning systems in a balanced and regulated manner (homoeostasis).
- lung function
- circulatory changes
- endocrine function
- gastrointestinal tract function
- kidney function
Glucocorticoids - have an important role in the preparation for birth, including involvement in lung and cardiac development, and the maturation of enzymes in a variety of pathways.
- Lungs at birth collapsed and fluid-filled - replaced with air by powerful inspiratory movement and absorption through the alveoli
- Lung epithelia has to rapidly change from its prenatal secretory function to that of fluid absorbtion.
- initiated by a late fetal change in alveolar epithelial cell (AEC) chloride and fluid secretion to sodium and fluid absorption.
- absorption requires sodium-potassium ATPase (Na-K-ATPase) together with apical sodium entry mechanisms (Epithelial Sodium Channels, ENaC)
- Fetal thyroid hormone is thought to have a hormonal role in this developmental switch
- These changes and pressure also lead to the pulmonary sytem becoming activated and changes in the circulatory shunting that existed before birth.
- During the late fetal period regular fetal breathing movements (FBM) also occur preparing both the skeletomuscular sysyem and lungs mechanically for respiration.
- Respiratory Rate is higher than adult (30 breaths/minute).
- Rib Orientation - Infant rib is virtually horizontal, allowing diaphragmatic breathing only. Adult rib orientation is oblique (both anterior and lateral views), allows for pump-handle and bucket handle types of inspiration.
- Umbilical Vasculature - The umbilical blood vessel cavity is lost postnatally over the course of weeks to months after birth. The adult anatomical remnant of the umbilical vein between the umbilicus and liver is the ligamentum teres.
- Foramen Ovale - two separate forms of foramen ovale closure; functional and structural. Functional closure begins at the first breath and is rapid. Structural (anatomical) closure is much slower and generally occurs before the end of the first year.
- Ductus Arteriosus - a direct connection between the pulmonary trunk and the dorsal aorta. Postnatal closure occurs initially by by smooth muscle contraction and begins at the first breath and is rapid, completed within the first day (about 15 hr after birth). Anatomical closure is much slower occuring by 2–3 weeks after birth (33% of infants), by 2 months (90% of infants) and by 1 year (99% of infants). The adult anatomical remnant of the ductus arteriosus is the ligamentum arteriosum.
- Ductus Venosus - connects portal and umbilical blood to the inferior vena cava. Functional closure occurs postnatally within hours. Structural closure commences days after birth and completes by 18 to 20 days. The adult anatomical remnant of the ductus venosus is the ligamentum venosum (a dorsal fissure on the liver).
Measured at one and five minutes after birth the Score values are totalled for all indicators: 7-10 is considered normal, 4-7 may require resuscitative measures, 3 and below require immediate resuscitation.
In recent years there has been some controversy of the relevance and accuracy of some of the criteria used in this test, though many feel it is still an invaluable initial assessment tool particularly where medical services are limited.
|Indicator||Score 0||Score 1||Score 2|
|Activity (muscle tone)||Limp; no movement||Some flexion of arms and legs||Active motion|
|Pulse (heart rate)||No heart rate||Fewer than 100 beats per minute||At least 100 beats per minute|
|Grimace (reflex response)||No response to airways being suctioned||Grimace during suctioning||Grimace and pull away, cough, or sneeze during suctioning|
|Appearance (color)||The baby's whole body is completely bluish-gray or pale||Good color in body with bluish hands or feet||Good color all over|
|Respiration (breathing)||Not breathing||Weak cry; may sound like whimpering, slow or irregular breathing||Good, strong cry; normal rate and effort of breathing|
Reference: Apgar, V. A proposal for a new method of evaluation of the newborn infant. Curr Res Anesth Analg. 1953 Jul-Aug;32(4):260-7. PMID:13083014
- Blood is collected using a heelprick and spotted onto a test sheet to dry for later testing.
- Different countries and medical services have different policies on not only what will be diagnostically tested, but also how long the test card will be kept following analysis.
Routine Screened Disorders
- Biotinidase Deficiency (OMIM)
- Congenital Adrenal Hyperplasia (CAH) (OMIM)
- Congenital Hypothyroidism (CH)
- Congenital Toxoplasmosis
- Cystic Fibrosis (CF) (OMIM)
- Galactosemia (GAL) (OMIM)
- Homocystinuria (OMIM)
- Maple Syrup Urine Disease (MSUD) (OMIM)
- Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCAD) (OMIM)
- An electrocardiogram (ECG / EKG) is an electrical recording of the heart which may identify electrical disorders including long QT syndrome.
- Non-specific hip instability is a common finding in newborns, particularly in females.
- More than 80% of clinically unstable hips at birth resolve spontaneously. Screening newborns for Developmental dysplasia of the hip (DDH) shows an incidence in infants between 1.5 and 20 per 1000 births. This incidence is influenced by several factors (diagnostic criteria, gender, genetic and racial factors, and age of the population).
Links: Musculoskeletal Abnormalities- Congenital Dislocation of the Hip | [hipdyssyn.pdf Screening for Developmental Dysplasia of the Hip PDF] | Screening for developmental dysplasia of the hip. Evidence synthesis no. 42. Rockville, Md.: Agency for Healthcare Research and Quality http://www.ahrq.gov/downloads/pub/prevent/pdfser/hipdyssyn.pdf | U.S. Preventive Service Task Force. Screening for developmental dysplasia of the hip: recommendation statement. Am Fam Physician. 2006 Jun 1;73(11):1992-6.
- The incidence of significant permanent hearing loss is approximately 1-3/1000 newborns.
- Neonatal hearing screening is carried out in the USA, UK and in Australia (2002 NSW Statewide Infant Screening Hearing Program, SWISH) There is a general guide giving a timetable for a number of simple responses that a neonate should make if hearing has developed normally.
- State Wide Infant Screening Hearing Program (SWISH) a newborn hearing testing program using an automated auditory response technology (AABR). Program was introduced in NSW Australia in 2002 across 17 area health service coordinators. It is thought that in NSW 86,000 births/year = 86-172 babies potentially born with significant permanent hearing loss.
- Automated Auditory Brainstem Response (AABR) uses a stimulus which is delivered through earphones and detected by scalp electrodes. The test takes between 8 to 20 minutes and has a sensitivity 96-99%.
|Year||< 34 weeks %||34-36 weeks %||total preterm %|
Data from: Prevention of preterm birth: a renewed national priority Damus K. Curr Opin Obstet Gynecol. 2008 Dec;20(6):590-6 PMID: 18989136
Perinatal care at the borderlines of viability: a consensus statement based on a NSW and ACT consensus workshop (February 2005) published in The Medical Journal of Australia 2006; 185 (9): 495-500.
- < 23 weeks survival is minimal and the risk of major morbidity is so high that initiation of resuscitation is not appropriate.
- 23 weeks active treatment may be discussed, but would be discouraged in NSW/ACT neonatal intensive care units.
- 23 to 25 weeks otherwise normal infant, there is an increasing obligation to treat. However, it is acceptable medical practice not to initiate intensive care if parents so wish, following appropriate counselling.
- 24 weeks antenatal transfer to a tertiary centre for fetal reasons is indicated. The option of non-initiation of intensive care/resuscitation should be offered.
- 25 weeks active treatment is usually offered, but the option of non-initiation of intensive care/resuscitation (presence of adverse fetal factors such as twin-to-twin transfusion, intrauterine growth restriction or chorioamnionitis) should also be discussed.
- 26 weeks + otherwise normal infant the obligation to treat is very high, and treatment should generally be initiated unless there are exceptional circumstances.
There are many birth associated abnormalities, only a few examples are listed below. (More? Abnormal Development)
- Premature Labor - occurs 7 -10% in humans, contributes 75% perinatal mortalities
- Underdeveloped Systems - particularly respiratory, surfactant, hyaline membrane disease (see respiratory development lecture)
- placenta accreta - abnormal adherence, with absence of decidua basalis
- placenta percreta - villi penetrate myometrium
- placenta previa - placenta overlies internal os of uterus, abnormal bleeding, cesarian delivery
- Historically, breech-born children were called agrippi, meaning "delivered with difficulty" (aegre parti).
- Breech position - occurs in about 3% of fetuses when buttocks or lower limb are presented to the birth canal rather than normal cephalic (head-first) position (presentation).
- Associated increased - perinatal mortality, perinatal morbidity, recurrence in successive siblings
Current research suggests that genetically that both men and women delivered in breech presentation at term could also contribute to an increased risk of breech delivery in their offspring. ([#18369204 Nordtveit TI, etal., 2008])
Meconium aspiration syndrome
- meconium is formed from gut and associated organ secretions as well as cells and debris from the swallowed amniotic fluid.
- Meconium accumulates during the fetal period in the large intestine (bowel). It can be described as being a generally dark colour (green black) , sticky and odourless.
- Normally this meconium is defaecated (passed) postnatally over the first 48 hours and then transitional stools from day 4.
- Abnormally this meconium is defaecated in utero, due to oxygen deprivation and other stresses. Premature discharge into the amniotic sac can lead to mixing with amniotic fluid and be reswallowed by the fetus. This is meconium aspiration syndrome and can damage both the developing lungs and placental vessels.
Occurs postnatally in mainly in premature and low birth weight infants (1 in 2,000 - 4,000 births). The underdeveloped gastointestinal tract appears to be susceptible to bacteria, normally found within the tract,to spread widely to other regions where they damage the tract wall and may enter the bloodstream.
Stillbirth and Perinatal Death
Perinatal period is the early postnatal period relating to the birth, statistically it includes the period up to 7 days after birth. Neonatal period is the four weeks/month after birth. Stillbirth and Perinatal Death
In New South Wales (2002) 613 perinatal deaths were reported.
- Unexplained antepartum deaths: 26.3% of perinatal deaths (or 39.2% of stillbirths)
- Spontaneous preterm labour: 20.6% (less than 37 weeks gestation)
- Congenital abnormality: 16.8%
- Antepartum haemorrhage: 8.5%
- Specific perinatal conditions: 7.3%, of which twin-twin transfusion accounted for 2.3% of deaths
- Hypertension (high blood pressure): 5.5%
- Perinatal infection: 4.4%
- Maternal disease: 4.4%
- Hypoxic peripartum death: 3.8%
Neonatal deaths (four weeks/month after birth)
- extreme prematurity was most common cause (39.6%)
- congenital abnormality (19.3%)
- neurological disease (13.4%)
- cardio-respiratory conditions (11.9%)
- infection (8.4%)
Data: Report of the New South Wales Chief Health Officer, 2004 accessed 19Oct05
- UNSW Embryology Introduction | Birth Overview | Abnormalities | Caesarean | Apgar | Premature | Low Birth Weight | Placental Cord Clamping | Cardiovascular | Stillbirth and Perinatal Death | Molecular Web Links
- Birth Statistics Australian Birth Statistics | International and Australian Population Statistics | WHO Normal Population Statistics | WHO Fact Sheets | Global Perinatal and Maternal Causes of Death | Population Comparisons between Countries | Developed and developing | Australian neighbours | Australian Trading Partners
amniotomy - birth medical procedure thought to speed labor, where the amniotic sac is artificially ruptured using a tool (amniohook).
breech - fetal buttocks presented first and can also occur in different forms depending on presentation (complete breech, frank breech, footing breech, knee breech).
decidual activation - increased uterine proteolysis and extracellular matrix degradation.
dilatation - opening of the cervix in preparation for birth (expressed in centimetres).
effacement - shortening or thinning of the cervix, in preparation for birth.
forceps - mechanical "plier-like" tool used on fetal head to aid birth.
fetal macrosomia - clinical description for a fetus that is too large, condition increases steadily with advancing gestational age and defined by a variety of birthweights. In pregnant women anywhere between 2 - 15% have birth weights of greater than 4000 grams (4 Kg, 8 lb 13 oz).
membrane rupture - breaking of the amniotic membrane and release of amniotic fluid (water breaking).
morbidity - (Latin, morbidus = "sick" or "unhealthy") refers to a diseased state, disability, or poor health due to any cause.
presentation - how the fetus is situated in the uterus.
presenting part - part of fetus body that is closest to the cervix.
second stage of labour - passage of the baby through the birth canal into the outside world.
Vacuum Extractor - suction cap device used on fetal head to aid birth.
Vertex Presentation (cephalic presentation) where the fetus head is the presenting part, most common and safest birth position.
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Course Content 2009
Embryology Introduction | Cell Division/Fertilization | Cell Division/Fertilization | Week 1&2 Development | Week 3 Development | Lab 2 | Mesoderm Development | Ectoderm, Early Neural, Neural Crest | Lab 3 | Early Vascular Development | Placenta | Lab 4 | Endoderm, Early Gastrointestinal | Respiratory Development | Lab 5 | Head Development | Neural Crest Development | Lab 6 | Musculoskeletal Development | Limb Development | Lab 7 | Kidney | Genital | Lab 8 | Sensory - Ear | Integumentary | Lab 9 | Sensory - Eye | Endocrine | Lab 10 | Late Vascular Development | Fetal | Lab 11 | Birth, Postnatal | Revision | Lab 12 | Lecture Audio | Course Timetable
Cite this page: Hill, M.A. (2021, April 20) Embryology 2009 Lecture 23. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_23
- © Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G