Chapter 28 The Normal Baby

General characteristics

Appearance

Salient points relating to the newborn baby’s general appearance are listed in Box 28.1.

Box 28.1 The appearance of the newborn baby

• Weight is highly variable but is normally around 3.5 kg

• Length is in the region of 50 cm from the crown of the head to the heels

• Occipitofrontal head circumference is 34–35 cm

• In an attitude of flexion, with arms extended, babies’ fingers reach upper thigh level

• Vernix caseosa, a white sticky substance, is present on the baby’s skin at birth

• Lanugo, downy hair, covers areas of the skin

• Colour is according to ethnic origin

• Cartilage of the ears is well formed

• Milia, distended glands in the skin, are often found over nose and cheeks

Physiology

Respiratory system

The normal baby has a respiratory rate of 40–60 breaths per minute.

Breathing is diaphragmatic, the chest and abdomen rising and falling synchronously.

The breathing pattern is erratic. Respirations are shallow and irregular, being interspersed with brief 10–15-second periods of apnoea. This is known as periodic breathing.

Babies are obligatory nose breathers and do not convert automatically to mouth breathing when nasal obstruction occurs.

Babies have a lusty cry, which is normally loud and of medium pitch.

Cardiovascular system and blood

The heart rate is rapid: 110–160 beats per minute.

Blood pressure fluctuates from 50–55/25–30 mmHg to 80/50 mmHg in the first 10 days of life.

The total circulating blood volume at birth is 80 ml/kg body weight.

The haemoglobin (Hb) level is high (13–20 g/dl), of which 50–85% is fetal Hb.

Breakdown of excess red blood cells in the liver and spleen predisposes to jaundice in the first week.

Vitamin K-dependent clotting factors II (prothrombin), VII, IX and X are low.

Platelet levels equal those of the adult but there is a reduced capacity for adhesion and aggregation.

Temperature regulation

The baby’s normal core temperature is 36.5–37.3°C. A healthy, clothed, term baby will maintain this body temperature satisfactorily, provided the environmental temperature is sustained between 18 and 21°C, nutrition is adequate and movements are not restricted by tight swaddling.

Renal system

The glomerular filtration rate is low and tubular reabsorption capabilities are limited. The baby is not able to concentrate or dilute urine very well in response to variations in fluid intake nor compensate for high or low levels of solutes in the blood. The first urine is passed at birth or within the first 24 hours, and thereafter with increasing frequency as fluid intake rises.

The urine is dilute, straw coloured and odourless.

Cloudiness caused by mucus and urates may be present initially until fluid intake increases.

Urates may cause pink staining, which is insignificant.

Gastrointestinal system

The mucous membrane of the mouth is pink and moist. The teeth are buried in the gums and ptyalin secretion is low. Small epithelial pearls are sometimes present at the junction of the hard and soft palates. Sucking pads in the cheeks give them a full appearance. Sucking and swallowing reflexes are coordinated.

The stomach has a small capacity (15–30 ml), which increases rapidly in the first weeks of life. The cardiac sphincter is weak, predisposing to regurgitation or posseting. Gastric acidity, equal to that of the adult within a few hours after delivery, diminishes rapidly within the first few days and by the 10th day the baby is virtually achlorhydric, which increases the risk of infection. Gastric emptying time is normally 2–3 hours.

The gut is sterile at birth but is colonised within a few hours. Bowel sounds are present within 1 hour of birth. Meconium, present in the large intestine from 16 weeks’ gestation, is passed within the first 24 hours of life and is totally excreted within 48–72 hours.

This first stool is blackish–green in colour, is tenacious and contains bile, fatty acids, mucus and epithelial cells.

From the  3rd to the 5th days the stools undergo a transitional stage and are brownish–yellow in colour.

Once feeding is established, yellow faeces are passed.

The consistency and frequency of stools reflect the type of feeding.

Breast milk results in loose, bright yellow and inoffensive acid stools. The baby may pass 8–10 stools a day or alternatively pass stools as infrequently as every 2 or 3 days.

The stools of the bottle-fed baby are paler in colour, semiformed and less acidic, and have a slightly sharp smell.

Physiological immaturity of the liver results in low production of glucuronyl transferase for the conjugation of bilirubin. This, together with a high level of red cell breakdown and stimulation of hepatic blood flow, may result in a transient jaundice which is manifest on the  3rd to 5th days. Glycogen stores are rapidly depleted, so early feeding is required to maintain normal blood glucose levels (2.6–4.4 mmol/l). Feeding stimulates liver function and colonisation of the gut, which assists in the formation of vitamin K.

Immunological adaptations

Neonates demonstrate a marked susceptibility to infections. The baby has some immunoglobulins at birth. There are three main immunoglobulins – IgG, IgA and IgM.

Only IgG is small enough to cross the placental barrier. It affords immunity to specific viral infections. At birth the baby’s levels of IgG are equal to or slightly higher than those of the mother. This provides passive immunity during the first few months of life.

IgM and IgA do not cross the placental barrier but can be manufactured by the fetus. Levels of IgM at term are 20% those of the adult, taking 2 years to attain adult levels. (Elevation of IgM levels at birth is suggestive of intrauterine infection.) Breast milk, especially colostrum, provides the baby with IgA passive immunity.

The thymus gland, where lymphocytes are produced, is relatively large at birth and continues to grow until 8 years of age.

Reproductive system: genitalia and breasts

In boys, the testes are descended into the scrotum by 37 weeks. The urethral meatus opens at the tip of the penis and the prepuce is adherent to the glans.

In girls born at term, the labia majora normally cover the labia minora. The hymen and clitoris may appear disproportionately large.

In both sexes, withdrawal of maternal oestrogens results in breast engorgement sometimes accompanied by secretion of ‘milk’ by the 4th or 5th day. Baby girls may develop pseudomenstruation for the same reason. Both boys and girls have a nodule of breast tissue around the nipple.

Skeletomuscular system

The muscles are complete, subsequent growth occurring by hypertrophy rather than by hyperplasia. The long bones are incompletely ossified to facilitate growth at the epiphyses. The bones of the vault of the skull also reveal lack of ossification. This is essential for growth of the brain and facilitating moulding during labour. Moulding is resolved within a few days of birth.

The posterior fontanelle closes at 6–8 weeks.

The anterior fontanelle remains open until 18 months of age, making assessment of hydration and intracranial pressure possible by palpation of fontanelle tension.

Psychology and perception

The newborn baby is alert and aware of his or her surroundings when awake.

Special senses

Vision

Babies are sensitive to bright lights, which cause them to frown or blink. They demonstrate a preference for bold black and white patterns and the shape of the human face, focusing at a distance of approximately 15–20 cm. No tears are present in the eyes of the newborn; therefore they become infected easily.

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1. The Placenta
2. Prolonged Pregnancy and Disorders of Uterine Action
3. The Third Stage of Labour
4. Problems of Pregnancy

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