Table 1

Prenatal, perinatal, and early postnatal sex differences in lung growth and development

Age	Development period	Morphology and physiology	Sex differences in morphology, maturation, and physiology
Prenatal^1-150
1–5 weeks	Embryonic33	Morphology: Lung bud formation24 33
6 to ∼15 weeks		Pseudoglandular33		Morphology: Differentiation of airways; airway branching pattern complete by 16 weeks24; airways smooth muscle appears in trachea and starts to contract spontaneously38
6 to ∼15 weeks		Pseudoglandular33		Ciliated goblet cells appear at ∼12 weeks15 38
16 to ∼26 weeks		Canalicular33		Morphology: Vascularisation occurs: acini develop24; Clara cells appear by 26th week15 24 38; fetal respiration begins to influence lung development41 44 45		Morphology: No sex differences in relationship of lung growth to somatic growth40
16 to ∼26 weeks		Canalicular33				Maturation: Mouth movements in female more advanced than male fetus34
26 to ∼36 weeks		Saccular33		Morphology: Alveoli first appear at 30 weeks and are uniformly present at 36 weeks; air space wall thickness declines rapidly after 28 weeks15 38	Morphology: See above40 Maturation: See above: also female fetus approximately 1.5 weeks ahead of male in lung phospholipid profiles which reflect surfactant production and maturation44 46
26 to ∼36 weeks		Saccular33		Rapid increase in lung volume40
Perinatal and postnatal
36–40 weeks				Morphology: Alveolar multiplication occurs24	Morphology: See above under 16 to ∼26 weeks40
				As gestation advances bronchial smooth muscle increases relative to size of airway38		Maturation: More advanced in female than male lungs: see above under 16 to ∼26 and 26 to ∼36 weeks
						Physiology: Female lungs have lower specific airway resistance than male lungs39
Birth to ∼1 week			Morphology: Proportion of goblet to ciliated cells increases.38 Rapid alveolar multiplication continues.33 Proportion of goblet to ciliated cells increases rapidly38 Physiology: Neonates have proportionately larger airways relative to lung volume (FRC),27 higher size corrected forced expiratory flow rates40 41 43 and lower specific airway resistance than older infants39	Morphology: Female lungs smaller than male lungs, may have fewer respiratory bronchioles24 Maturation: More advanced in female than male lungs,44 46 premature female lungs less at risk for RDS44 and transcient tachypnoea of the newborn47 than male lungs and more responsive to hormone accelerators of surfactant production44 Physiology: As above under 36–40 weeks39
1 to ∼52 weeks			Morphology: Formation of single capillary network occurs and alveolar multiplication continues,33 growth more or less linear with age at least up to age 224 Physiology: Airway resistance increases rapidly to adult levels in the first year of life39	Morphology: See above under birth to 1 week15 24 Maturation: Female lungs more responsive than male lungs to hormones44 Physiology: See above under 36–40 weeks,39 female infants also have higher absolute as well as size corrected forced expiratory flow rates than male infants40

Compiled from references 15, 24, 27, 33, 34, 38–41, 44–46.
↵1-150 Prenatal age expressed as weeks after conception.