Neonatal physiology

Key points

Antenatal diagnosis

Chorionic Villus Sampling 11-14 weeks

Amniocentesis - 15 weeks onwards

NIPT - non-invasive prenatal diagnosis - circulating foetal DNA for chromosomal abnormalities e.g., Trisomy 21

Antenatal Counselling

In the UK, at least 2 antenatal scans are routinely performed.  First around 12 weeks of gestation known as dating scan and the second around 20 weeks of gestation known as the anomaly scan.  If indicated, further scans are performed. 

If a surgical condition in the foetus is identified, a neonatal surgeon can be involved in antenatal counselling. It allows the clinicians to prepare for the medical and psychological needs of the parents, foetus, and newborn before, during and after delivery.

If possible, it would be helpful for the neonatal surgeon to attend the scan to review the images with the foetal medicine doctor and speak to the family afterwards.  Sometimes, the counselling can be done during further scans.  Otherwise, a face to face clinic or a virtual clinic can be arranged. 

The 7 principles of Antenatal Counselling:

I. Diagnosis, Differential Diagnosis and Measurements

II. Aetiology, Associations and Effects

III. Further scans, Frequency of scans and frequency of surgical consultations

IV. Antenatal therapy, interventions and surgery

V. Delivery: Time, Mode and Place

VI. Post natal management: Immediate, Medical, Surgical

VII. Closure: Information leaflets, parental visit to NICU, Letter

I. Diagnosis, Differential Diagnosis and Measurements

A. Diagnosis

The following are some of the conditions the neonatal surgeon may be involved in antenatal counselling:

Gastroschisis, Exomphalos, Congenital Diaphragmatic Hernia, Oesophageal Atresia, Duodenal Atresia, Small Bowel Atresia,  Echogenic Bowel, Cervical Teratoma, Lymphatic Malformations,  Intra-abdominal cysts, Primary antenatal foetal hydrothorax, Spinal Bifida, Sacrococcygeal Teratoma, Urological conditions,

B.  Differential Diagnosis

Examples: 

• Gastroschisis vs Ruptured Exomphalos

• CDH vs CPAM

• Lymphatic vs Vascular malformations

• Duplication cysts vs Ovarian cysts

C. Measurements

See summary of important scoring systems below

II. Aetiology, Associations and Effects

A.  Aetiology: Smoking, marijuana, alcohol

B.  Associations: Chromosomal, Cardiac.

C.  Effects: 

Polyhydramnios, oligohydramnios

Bowel dilatation

Pulmonary hypoplasia

Hydrops (fluid collection in 2 or more compartments - Pericardium, pleura, peritoneum, skin)

III. Further Scans

A. Foetal MRI, foetal echocardiogram

B. Frequency of scans: As indicated; usually 2-4 weekly

C. Frequency of surgical consultations: as necessary

IV. Antenatal Treatment

A. Foetal Therapy:  Laser, sclerotherapy , radiotherapy, steroids

B. Foetal Intervention e.g., Cyst aspiration, tracheal occlusion

C. Foetal Surgery e.g., CPAM excision

V. Delivery

A. Timing of delivery: Term, preterm (MDT with neonatologist, neonatal surgeon and foetal medicine team)

B. Mode of delivery: Normal vaginal delivery, C-section

C. Place of delivery: Home, hospital, tertiary centre

VI.  Postnatal plan

A.  Immediate post natal plan:  NBM, Elective intubation, etc

B.  Medical plan:  Intravenous access, Bloods, etc

C.  Surgical Management:  operation, timing, post op course

VII. Closure

A. Information leaflets, websites, social media

B. Offer couple to visit the NICU

C. Dictate letter ( Couple, GP, Foetal medicine team and Neonatal Team )

Written by Prof. Ashok Daya Ram MBBS, FRCS, FRCPS, FRCS(Paed Surgery), FEBPS

Summary of important antenatal scoring systems

Sacrococcygeal teratoma

Tumour to foetal weight ratio

Tumour measured in 3 dimensions, divided by foetal weight measured on USS

If >0.12 = 80% hydrops and 60% mortality

If <0.12 = 100% survival

Exomphalos diameter (ED)/Abdominal circumference ratio

>0.24 concerning for increased likelihood of staged closure, ventilation, hospital stay

CDH

Lung head ratio = On USS at level of 4 chamber view of heart: Measure 2 longest perpendicular diameters of CONTRALATERAL lung in mm and multiply them

Divide by head circumference in mm

If >1.35 = 100% survival

If 0.6-1.35 = 60%

If <0.6% = 0%

CPAM volume ratio

3 longest measurements of lesion on USS multiplied together, then multiplied by 0.52, then divided by head circumference

If CVR is <1.6, only 2% risk of hydrops

If >1.6 80% chance of hydrops

Definitions

Small for gestational age: <10th percentile

Large: >90th percentile

Asymmetrical SGA: Insult late in pregnancy, at particular risk of complications

Extreme low birthweight <1kg

Very low <1.5kg

Low birthweight <2.5kg

Inadequate birthweight <3kg

Adequate birthweight 3-4kg

Macrosomic >4kg

Prematurity:

Extremely preterm < 28 weeks

Very preterm 28 - 31 weeks

Moderate preterm 32 - 36 weeks

Term 37 weeks

28-day survival rates in prematurity:

22 weeks ~10-20%

24 weeks ~ 60%

34 weeks ~ equivalent survival to full term

Echogenic Bowel

Definition: Increased brightness of the foetal bowel where the echogenicity of bowel is similar to or greater than that of the adjacent bone at the time of the second trimester USS

Focal type is more pathogenic than diffuse type

Echogenicity of normal bowel increases throughout pregnancy

The finding of echogenic bowel becomes normal in the third trimester

Isolated anomaly have no clinical sequelae in 85% of cases

Increased risk of aneuploidy (3-30%)

Bowel injury from a variety of causes

Foetus is potentially at risk for poor growth

Associated conditions:

Aneuploidy, Atresia, Anaemia

Bleeding (swallowed blood)

Cystic Fibrosis

Impending foetal demise

Intrauterine growth restriction (IUGR)

Infection (CMV, Toxoplasmosis, Parvovirus)

Grading of Echogenic Bowel:

Grade 0: < liver (normal)

Grade 1: > liver, < bone (normal)

Grade 2: = bone (potentially abnormal)

Grade 3: > bone (potentially abnormal)

Work up of Echogenic Bowel

Detailed ultrasonogram of the foetus

Amniocentesis for karyotype

CF carrier typing of parents

Maternal serologic testing for recent cytomegalovirus and toxoplasmosis

Follow-up with serial growth scans

Written by Prof. Ashok Daya Ram MBBS, FRCS, FRCPS, FRCS(Paed Surgery), FEBPS

Twin to twin Transfusion Syndrome

Definition: A serious progressive disorder in monochorionic di-amniotic twinswhere one twin transfuses another through abnormal or imbalanced blood vessel connections in the shared placenta

Twins do not have malformations

80% Mortality

Effects on the recipient twin:

• Polycythaemia

• Hypertension

• Polyuria

• Polyhydramnios

• Circulatory overload

• Heart Failure

• Hydrops Fetalis

• Foetal Demise

Effects on the donor twin:

• Anaemia

• Hypotension

• Oliguria

• Oligohydramnios

• Circulatory insufficiency

• Growth restriction

• Renal Failure

• Foetal Demise

Maternal mirror syndrome:

• Vomiting

• Hypertension

• Generalised Oedema

• Pulmonary Oedema

• Proteinuria

Management:

A. Amnioreduction

B. Fetoscopic Laser Ablation of vessels:

• Transumbilical

• Examine the blood vessels on the placental surface directly

• Abnormal vascular connections between the twins is ablated by directing a laser beam at them

Written by Prof. Ashok Daya Ram MBBS, FRCS, FRCPS, FRCS(Paed Surgery), FEBPS

Physiology

Term baby grows 25-30g per day

10-20g per day for premature babies

Primitive reflexes disappear at 4-6 months

Neonatal renal function

Born in water overload inversely proportional to gestation

Neonatal kidneys unable to regulate water balance

Unable to retain or excrete sodium based on deficiency or overload

Hypoglycaemia in neonates

Seizure and coma

Low glycogen stores and high metabolic rate

No gluconeogenesis, depends on glycolysis

Hyperglycaemia in neonates

Insulin resistance and deficiency

Associated with TPN

Retinopathy of prematurity

Vascular immaturity, leaks. Abnormal angiogenesis

O2 exposure is risk factor

Screen all infants <1.5kg and <32/40, or larger babies that have been unstable requiring O2

Needs laser photo coagulation

Development of the lungs:

Embryonic phase week 3

Pseudoglandular phase 5-17 weeks

Cannalicular phase 16-25 weeks

Terminal saccular phase 24 weeks to birth

Alveolar phase birth to childhood

Surfactant secreted by type 2 pneumocytes

Worse outcomes when exogenous surfactant used in CDH

Pre-ductal (monitor on right hand) and post-ductal (monitor on either foot) O2 saturation monitoring - difference of ≥10% suggests right to left shunting requiring investigation

Blood volume in neonates ~85ml/kg

Blood volume in children/adults ~70ml/kg

Foetal Hb O2 dissociation curve in neonates to left of adults i.e. accepts O2 more readily, does not release easily

Curve normalises by 4-6 months of age

Mechanisms of immunodeficiency in neonates

IgA and IgM do not cross placenta

Small pool of neutrophils

Inability to differentiate plasma cells and produce antibodies

Treatments: IgG, G CSF

Intraventricular haemorrhage

Germinal matrix haemorrhage-intraventricular haemorrhage is the commonest cause

45% of infants born less than 750 g having a haemorrhage

Blood enters the lateral ventricles causing CSF obstruction, then ventricular dilatation

Infarction can break down to form a porencephalic cyst

Page edited by Mrs Charnjit Seehra BSc November 2024

Page edited by Prof. Ashok Daya Ram MBBS, FRCS, FRCPS, FEBPS, FRCS (Paed Surgery), Consultant Paediatric and Neonatal Surgeon, Norfolk and Norwich University Hospital, Norwich, UK. January 2025

References

Royal College of Obstetricians and Gynaecologists Green top guidance 8

Office of national statistics UK

Rodriguez MA, et al. Tumor volume to fetal weight ratio as an early prognostic classification for fetal sacrococcygeal teratoma. J Pediatr Surg. 2011 Jun;46(6):1182-5. doi: 10.1016/j.jpedsurg.2011.03.051. PMID: 21683219

Nitzsche K, Fitze G, Rüdiger M, Wimberger P, Birdir C. Prenatal diagnosis of exomphalos and prediction of outcome. Sci Rep. 2021 Apr 22;11(1):8752. doi: 10.1038/s41598-021-88245-0. PMID: 33888820; PMCID: PMC8062495.

https://perinatology.com/calculators/LHR.htm

https://perinatology.com/calculators/CVR.htm

Seaton SE, et al Estimated neonatal survival of very preterm births across the care pathway: a UK cohort 2016–2020 Archives of Disease in Childhood - Fetal and Neonatal Edition 2023;108:562-568.

Holcomb and Ashcraft’s Pediatric Surgery, 7th edition, 2020, Chapter 1

Rehman S, Bacha D. Embryology, Pulmonary. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing

Norfolk and Norwich Hospital Saturations monitoring in newborn guideline