Chapter 11 Labour and Birth PDF

CHAPTER 11 Labour and Birth Timing of Birth Typically pregnancy lasts just shy of 9 months. Using the 38 weeks as a guide from conception, gestational development lasts approximately 266 days. Birth within 2 weeks before or after the due date is generally considered normal. Human Reproductive Bio...

CHAPTER 11 Labour and Birth Timing of Birth Typically pregnancy lasts just shy of 9 months. Using the 38 weeks as a guide from conception, gestational development lasts approximately 266 days. Birth within 2 weeks before or after the due date is generally considered normal. Human Reproductive Biology, 4th Ed. (2014) pg. 205 Seasonal and temporal variation in when humans are born are likely remnants from ancestral species. Hormonal Initiation of Birth In humans, there is evidence to suggest that the timing of birth is initiated through hormonal signalling pathways. In particular, it appears that corticotropin-releasing hormone (CRH) secreted by the placenta may play a pivotal role. CRH triggers fetal pituitary and adrenal glands to secret androgens and cortisol. This stimulates increased estrogen synthesis in the carrier. https://www.news-medical.net/health/CorticotropinReleasing-Hormone.aspx Carrier Estrogen and Progesterone Progesterone, which is high during pregnancy prevents myometrium contractions by inhibiting the synthesis of prostaglandins and cortisol receptors, and by reducing the number of calcium channels in uterine tissues. Estrogen has the opposite effect on these systems. Estrogens also increase gap junctions between myometrial smooth muscle fibres and soften the collagen of the cervix. Progesterone doesn’t generally drop markedly at the end of pregnancy, but the amount of estrogen does rise. Prostaglandins and Oxytocin A higher E/P ratio promotes the production of prostaglandins. Their role is likely to act as paracrine factors to promote uterine contractions. Oxytocin is the hormone most directly involved in uterine contractions during labour. https://www.frontiersin.org/articles/10.3389/fendo.2021.742236/full High E/P may trigger placenta to secret oxytocin and increase the number of oxytocin receptors. Like CRH, oxytocin and prostaglandins engage in positive feedback loops. Human Reproductive Biology, 4th Ed. (2014) pg. 210 Induced Labour Labour may be induced, artificially forced forward, before or at, or after the due date. As a first step to try and trigger labour to happen without hormonal intervention, the medical practitioner will puncture the amniotic sac. Generally involves the administration of synthetic forms of oxytocin and prostaglandins. Often administered intravenously, but can be triggered to release naturally through manual stimulation (oxytocin). Preparing for Labour To prepare its self for labour, the carrier’s body will under several shifts prior to birth. • The abdomen may decrease in size as the fetus moves farther down in the pelvis (lightening). • More frequent urination. • Head of fetus will move into the pelvic girdle. Preparation is important as labour may last up to 24 hours! Human Reproductive Biology, 4th Ed. (2014) pg. 212 1. Cervical Effacement and Dilation May be preceeded by false contractions a.k.a Braxton-Hicks contractions. When true contractions begin, intense contractions at regular intervals, the cervix begins to efface. Early contractions are milder, and increase in intensity and length further into labour. Prior to effacement commencing, the mucous plug will be dislodged and the amniotic sac may tear/rupture. Early dilation (up to 7cms) begins when contracts are only 1-3 minutes apart, this is the beginning of active labour. Transition dilation occurs between 7 – 10 cm. Generally very intense, but typically the shortest part of labour. Full dilation occurs at 10 cm. Carrier is now prepped for delivery. Human Reproductive Biology, 4th Ed. (2014) pg. 215 Human Reproductive Biology, 4th Ed. (2014) Figure 11.5 pg. 214 2. Expulsion of Fetus Begins with full dilation and ends with fetal delivery. Contractions are generally reduced compared to transition phase of dilation. Lasts between 30 minutes – 2 hours. Carriers are encouraged to actively push during contractions (engage voluntary abdominals to support involuntary uterine contractions). When the fetus’ head crowns, birth is imminent. The shoulders come next and can be difficult to maneuver through the birth canal. The rest of the baby’s body follows soon after. Mucus/fluid is removed from the airways and the umbilical cord is clamped in two places 3 cm from the baby’s abdomen and cut. Human Reproductive Biology, 4th Ed. (2014) pg. 215 3. Expulsion of Placenta This final stage of the birthing process sees the placenta expelled from the carrier’s body. Generally lasts 5-30 minutes. Generally expelled from softer contractions after birth, sometimes abdominal massage is required to encourage expulsion. Typically ~250 ml of blood is lost during delivery, if hemorrhage occurs, oxytocin or vasoconstricting medications can be administered. Various uses of the placenta exist, including the harvesting of hematopoietic stem cells which can be used to treat some blood cancers. Preterm Babies Preterm is used to describe a baby born before 35 weeks of development. These babies are typically smaller, may have poorly developed organs, exhibit higher risk for neurological damage, and higher risk of neonatal death. Preterm babies represent ~8% of births in Canada. Currently detecting preterm birth is difficult but can involved measuring cervical length, levels of fetal fibronectin, and carrier blood levels of CRH (weeks 14-18). https://blog.frontiersin.org/2023/03/27/shh-intensive-care-incubators-resonatesounds-and-risk-damage-to-premature-babies-hearing-scientists-say/ Multiple Births On average, delivery of multiples occurs 22 days prior to the delivery of single births. Multiple babies may all present head first, or the second birthed may be breech. One multiple usually emerges a few minutes to an hour ahead of the other(s). Multiples born several days apart can happen, but is not thought to be linked to superfetation. Difficult Fetal Positions 95% of births involve the fetus in the “normal” position, with their head down into the pelvic girdle. In 3-4% of births the fetus is breech, and in 0.5% of births the fetus is in a transverse position during labour and delivery. Human Reproductive Biology, 4th Ed. (2014) pg. 219 Forceps and Vacuum Extraction Sometimes during delivery a fetus gets stuck in the birthing canal. This can be compromising for the fetus and carrier. In order to speed up the movement of the fetus, a medical professional may use forceps or vacuum extraction. Although vacuum extraction is less likely to cause damage to the genital tissues of the carrier, it is more likely to cause fetal scalp injury. Human Reproductive Biology, 4th Ed. (2014) Figure 11. 10 pg. 220 Cesarean (C-section) Delivery A procedure performed under general or spinal anesthetic in which a cut is created through the lower abdomen/pelvic to retrieve the fetus. Generally lasts between 20-90 minutes. Much of which is the suturing of the carrier. May be elective (scheduled) or emergency (not scheduled). Performed for numerous reasons (transitional position, small pelvis, large fetus, fetal distress, placenta previa, heart function irregularities). Cesarean deliveries account for ~28% of births in Canada. Recovery for a cesarean is arduous and carriers are often not provided with recovery time in line with other major abdominal surgeries. https://medlineplus.gov/ency/presentations/100191_3.htm Medications During Labour Medications provided during labour can be divided into two major categories: analgesics and anesthetics. Analgesics are pain relievers, while anesthetics are numbing agents (cause a loss of sensation). Conduction anesthetics are often used, the most common of which is an epidural block. Analgesics are often administered via intramuscularly or intravenously. Human Reproductive Biology, 4th Ed. (2014) pg. 221 “Natural” Birthing Methods Before recent times, most people gave birth with minimal to no medical intervention. Fetal and carrier death rates were much greater during these periods of time. Many people today opt for birth plans which restrict the use of therapeutic drugs and may involve birth outside of a hospital setting. https://www.pinterest.ca/pin/72972456450179124/ Why is Human Birth so Difficult? Compared to our closest relatives, and most other mammals, humans have terrible births. • Fetal head size too big for pelvis • Necessity for twisting through birth canal • Injury/infection in carrier perineum • Presentation with face down • Prolonged labour and delivery (34x longer than other primates) Human Reproductive Biology, 4th Ed. (2014) pg. 224