Pregnancy and childbirth

Explain what fertilisation is, in which part of the female reproductive system it normally occurs, and which cell results from it.

A hospital analyzes three cases of twin births (birth of two babies in the same delivery):

• Case 1: A boy and a girl with different blood types.

• Case 2: Two girls who share 100% of their DNA.

• Case 3: Two boys who physically look very similar, but genetic testing shows they only share 50% of their genes, just like two siblings born in different years.

1. a) Classify each case as identical twins (monozygotic) or fraternal twins (dizygotic), precisely deducing what occurred during fertilization in each one (number of fertilized eggs, number of sperm, and behavior of the zygote).
2. b) Someone claims: "In Case 1, the boy and the girl must have originated from a single egg that was fertilized simultaneously by two sperm: one with an X chromosome and another with a Y chromosome." Demonstrate why this statement is biologically erroneous and explain how sex was actually determined in that pair of babies.

Put the following stages in order from when the egg cell is fertilised until the baby is born, and write a brief sentence about what happens in each one: foetus, fertilisation, childbirth, zygote, embryo.

Explain the difference between embryo and foetus, state at what point in pregnancy the transition from one stage to the other occurs, and mention an important developmental change in each of the three trimesters of gestation.

Around the middle of pregnancy, an ultrasound scan can already show the baby's sex. Relate this fact to the moment when the organs are formed and differentiated, and explain why an ultrasound scan cannot show it at the beginning of pregnancy.

The neural tube is the embryonic structure that closes to give rise to the brain and spinal cord. For this closure to occur correctly, the embryo needs adequate levels of folic acid before day 28 after fertilization. Moreover, folic acid taken as a supplement needs several weeks to build up in the tissues to protective levels.

Imagine a woman with regular 28-day menstrual cycles who had her last menstrual period on November 1 and ovulated on November 14:

1. a) Assuming fertilization occurred on November 14, calculate the approximate date when the first missed menstrual period would take place (when the woman suspects pregnancy) and the date when the embryo's neural tube closes definitively.
2. b) Based on these dates, explain why starting to take folic acid only after getting a positive result on a pregnancy test is usually too late to prevent neural tube defects such as spina bifida.
3. c) Justify why health authorities recommend folic acid supplementation for any woman who is actively trying to conceive, and not only for those who have already confirmed they are pregnant.

Look at the image of the foetus inside the uterus. Locate the uterus, the placenta, the umbilical cord and the amniotic fluid, and explain the function of each of these structures in protecting and nourishing the foetus.

Explain what the amniotic sac is and cite two functions the amniotic fluid performs for the foetus.

State whether these statements are true or false and justify your answer: a) human pregnancy lasts about forty weeks; b) the mother's blood and the foetus's blood mix in the placenta; c) the umbilical cord connects the foetus to the placenta.

During pregnancy, the foetus develops inside the uterus attached to the placenta by the umbilical cord. Explain what functions the placenta performs for the foetus and reason why substances consumed by the mother (alcohol, tobacco, certain medications) can affect the baby's development.

In the placenta, the mother's blood and the foetus's blood do not mix, but nutrients, oxygen and waste products pass between them. Explain what type of exchange takes place across the membranes of the placenta and why it is important that the two bloods never mix.

A pregnant woman is said to have to "eat for two". Qualify that statement: explain whether energy needs really double, which nutrients are especially recommended to watch during pregnancy, and why.

Look at the following average data collected in a maternity and children's hospital:

• Single pregnancy (1 fetus): average duration = 40 weeks; average weight = 3.4 kg.

• Twin pregnancy (2 fetuses): average duration = 36 weeks; average weight = 2.4 kg per baby.

• Triplet pregnancy (3 fetuses): average duration = 32 weeks; average weight = 1.7 kg per baby.

1. a) Interpret the data: what relationship exists between the number of fetuses carried simultaneously, the timing of delivery, and the birth weight of the newborns?
2. b) Justify these results biologically, taking into account two limiting factors: the maximum stretching of the muscular wall of the uterus before triggering labor contractions, and the surface area for nutrient and gas exchange in the placenta.
3. c) Predict which two immediate clinical complications (related to breathing and maintaining body temperature) doctors will need to monitor as a priority in the newborns from the triplet delivery compared to the single pregnancy.

Gestational diabetes occurs when glucose levels in the mother's blood remain abnormally high. To understand its consequences on the fetus, consider how the placenta works:

• Glucose crosses the placenta by diffusion from maternal to fetal blood.

• Maternal insulin CANNOT cross the placenta.

• Around the fourth month of development, the fetal pancreas is already capable of producing its own insulin when it detects excess glucose. Insulin stimulates the storage of that glucose in the form of body fat and muscle.

1. a) Predict what will happen to the fetus's insulin production and its body development if the mother does not manage her diabetes during the second and third trimesters of pregnancy.
2. b) A student reasons: "Since the fetus receives so much glucose from the mother, upon birth and the cutting of the umbilical cord, it will have a dangerous excess of sugar in its blood." Refute this reasoning by explaining why, paradoxically, the newborn is at serious risk of hypoglycemia (a sudden drop in glucose) in the first hours after delivery.

A pregnant woman states: "My grandmother smoked a pack a day throughout all her pregnancies and my aunts and uncles were born completely healthy and strong, so smoking during pregnancy isn't as dangerous as they say."

To respond to her using the scientific method, analyze these data from thousands of births:

• Non-smoking mothers: average birth weight = 3.45 kg; rate of low birth weight newborns (< 2.5 kg) = 4.1%.

• Smoking mothers (> 10 cigarettes a day): average birth weight = 2.90 kg; rate of low birth weight newborns (< 2.5 kg) = 14.8%.

1. a) Refute the woman's argument by explaining the difference between an isolated anecdotal experience and statistical evidence based on the study of large populations.
2. b) Knowing that carbon monoxide from tobacco binds to hemoglobin preventing normal oxygen transport, and that nicotine narrows the blood vessels of the placenta, predict how these two mechanisms affect the supply of oxygen and nutrients to the fetal cells, and justify the difference in weight observed in the data.

Describe what happens during childbirth: which organ contracts to push the baby out, what path it follows to emerge, and what happens to the umbilical cord after birth.

Explain what labour contractions are, which organ produces them, and what they achieve.

Childbirth does not happen all at once: three stages are distinguished: the dilation stage of the cervix, the expulsion stage of the baby, and a final stage called the afterbirth (delivery of the placenta). Explain what happens in each of the three stages and what is expelled in the last one.

During intrauterine life, the fetal lungs are collapsed, filled with fluid, and do not perform gas exchange, as all oxygenation comes from the placenta through the umbilical vein. At the moment of birth, the umbilical cord is cut, and the newborn takes its first cry.

1. a) A relative observes the birth and comments: "We should prevent the baby from crying at birth, because crying exhausts it; it would breathe better in silence and calmly." Refute this statement by justifying the mechanical function that this first forced inspiration, which usually accompanies the cry, performs on the pulmonary alveoli and the fluid they contain.
2. b) Explain what change occurs in the concentration of gases (oxygen and carbon dioxide) in the baby's blood during the first few seconds after clamping the umbilical cord, and deduce how this change stimulates the nervous system to force it to take its first breath.
3. c) Design a flowchart with arrows connecting these four key steps in order: clamping of the umbilical cord / increase in carbon dioxide in the baby's blood / first cry and opening of alveoli / arrival of oxygenated blood via the pulmonary pathway to the entire body.

Explain what breastfeeding is and cite two advantages that breast milk provides to the newborn.

Describe two routine medical check-ups during pregnancy and explain what information each one provides about the health of the mother and the foetus.

Explain what a caesarean section is, in which situations it is decided to perform it, and reason why, although today it is a safe operation, it is reserved for cases in which vaginal delivery poses a risk.