Essential Neonatal Medicine

Sunil Sinha, Lawrence Miall, Luke Jardine

• Publisher: Wiley-Blackwell
• Year: 2017
• ISBN:
  9781119235750
• Edition: 6
• Topic: Médecine
• Subtopic: Pédiatrie

Providing a comprehensive yet concise guide for trainee doctors, neonatal nurses and midwives, Essential Neonatal Medicine continues to be an indispensable resource that combines the depth and breadth of a textbook with the efficiency of a revision guide.

Extensively updated and full-colour throughout, this edition includes new chapters on neonatal transport and palliative care, as well as further content on pathophysiology and embryology, quality improvement and risk management, infection control, and non-invasive ventilation.

With an improved artwork programme and a new glossary of terms, Essential Neonatal Medicine is ideal for all trainee health professionals new to neonatology, or looking for a comprehensive aid to support them.

CHAPTER 1
The fetus, placenta and changes at birth

Key topics

• Placental function
• Fetal homeostasis
• Fetal circulation
• Assessment of fetal well-being
• Screening during pregnancy
• Fetal monitoring during labour
• Fetal compromise

Introduction

The discipline of ‘perinatal medicine’ spans the specialities of fetal medicine and neonatology. The obstetrician must have a thorough knowledge of pregnancy and its effects on the mother and fetus, as well as fetal development and physiology. The neonatologist specialises in the medical care of the infant immediately after birth, but must also have a thorough understanding of fetal development and physiology. This chapter reviews fetal assessment and physiology to provide the paediatrician and neonatal nurse with a better understanding of normal perinatal adaptation, and the adverse consequences arising from maladaptation.

Placental function

The placenta is a fetal organ that has three major functions: transport, immunity and metabolism.

The uterus is supplied with blood from the uterine arteries, which dilate throughout pregnancy, increasing blood supply 10-fold by term. Maternal blood bathes the intervillous space and is separated from fetal blood by the chorionic plate. Transport of nutrients and toxins occurs at this level. Oxygenated fetal blood in the capillaries of the chorionic plate leaves the placenta via the umbilical vein to the fetus (Fig. 1.1).

Figure 1.1 Diagram of placental structures showing blood perfusion.

Transport

The placenta transports nutrients from the mother to the fetus, and waste products in the other direction. This occurs in a number of ways, including simple diffusion (for small molecules) and active transport, which is used for larger molecules. The placenta is crucially also responsible for gaseous exchange of oxygen and carbon dioxide. Oxygen diffuses from the mother (PO₂ = 10–14 kPa, 75–105 mmHg) to the fetus (PO₂ = 2–4 kPa, 15–30 mmHg), where it binds to fetal haemoglobin. This has a higher affinity for oxygen than maternal haemoglobin for a given PO₂. The dissociation of oxygen from maternal haemoglobin is also facilitated by a change in maternal blood pH.

Immunity

The placenta trophoblast prevents the maternal immune system from reacting against ‘foreign’ fetal antigens. Rejection does not occur because the trophoblastic cells appear to be non-antigenic, although it is known that fetal cells can cross into the maternal circulation where they can trigger an immune reaction (e.g. rhesus haemolytic disease). Maternal IgG antibody – the smallest of the immunoglobulins – can cross the placenta, where it provides the newborn with innate immunity to infectious diseases. These IgG antibodies can also cause perinatal disease such as transient hyperthyroidism (see Chapter 21).

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CLINICAL TIP

Because IgG antibody crosses the placenta, the presence of IgG antibody in the newborn’s blood does not necessarily mean it has been congenitally infected. This is of particular relevance when testing newborns for HIV infection, where a positive IgG may just reflect maternal exposure. Instead, direct tests (e.g. viral RNA by PCR) are required (see Chapter 10).

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Metabolism

The placenta is metabolically active and produces hormones, including human chorionic gonadotropin (hCG) and human chorionic thyrotropin (hCT). It also detoxifies drugs and metabolites. Oestriol cannot be produced by the placenta alone. This is done by the fetal liver and adrenal glands. The metabolites are then sulphated by the placenta to form oestrogens, one of which is oestriol.

Because of its metabolic activity, the placenta has very high energy demands and consumes over 50% of the total oxygen and glucose transported across it.

Fetal homeostasis

The placenta is an essential organ for maintaining fetal homeostasis, but the fetus is capable of performing a variety of physiological functions:

• The liver produces albumin, coagulation factors and red blood cells.
• The kidney excretes large volumes of dilute urine from 10–11 weeks’ gestation, which contributes to amn...