Prematurity remains a major cause of neonatal morbidity and mortality, largely due to underdeveloped lungs. Adequate maturation of the foetal lung is crucial for successful extrauterine survival, as it ensures proper gas exchange and respiratory function at birth. ¹ Lung development in utero proceeds through a series of histologically distinct stages: embryonic, pseudoglandular (5–16 weeks), canalicular (17–25 weeks), saccular (25–36 weeks), and alveolar (36 weeks to postnatal period). ^{2, 3, 4} Among these, the canalicular and saccular stages are particularly important for establishing vascular networks and initiating surfactant production both critical for viability in preterm neonates. ^{5, 6}

Despite advancements in neonatal care that allow for the survival of increasingly premature infants the degree of lung development remains the principal limiting factor. ⁷ Additionally, studies suggest significant inter-population differences in foetal growth and maturation, yet normative data derived from Indian populations remain scarce.^{8, 9} This gap poses challenges for clinicians and pathologists when estimating Fertilization age and evaluating foetal lung maturity in clinical or medico-legal contexts.

In this background, the present study was designed to evaluate the morphogenesis of human foetal lungs using a sample of aborted foetuses between 16 and 38 weeks of gestation. By examining morphological parameters such as crown–rump length (CRL), body weight, lung location, and external appearance, we aimed to characterize developmental trends and establish reference data reflective of regional foetal growth patterns.

Study Design and Setting: This descriptive cross-sectional observational study was conducted in the Department of Anatomy at a tertiary care teaching hospital in India over a two-year period from January 2022 to December 2023. The objective was to document the morphogenesis of human foetal lungs at various Fertilization ages using foetuses obtained from spontaneous abortions, medically indicated terminations, and stillbirths.

Ethical Clearance: The study was approved by the Institutional Ethics Committee (IEC). Written informed consent was obtained from the parents or legal guardians in accordance with national biomedical research guidelines and the provisions of the Medical Termination of Pregnancy (MTP) Act, 1971.

Sample Size and Selection Criteria: A total of 50 human foetuses ranging from 16 to 38 weeks of gestation, were included. The specimens were obtained in fresh condition from the Department of Obstetrics and Gynaecology immediately following expulsion.

Inclusion Criteria:

Exclusion Criteria:

Specimen Handling and Preservation: After collection, all foetuses were rinsed in phosphate-buffered saline (PBS) to eliminate blood and debris. They were then fixed in 10% neutral buffered formalin for a minimum of seven days. Each specimen was labelled with a unique identification number, and accompanying data included gestational age, foetal sex, maternal history, and LMP where available.

Fertilization age Determination: Fertilization age was estimated using two methods:

Morphological Assessment:

Observations were correlated with Fertilization age to identify stage-specific lung development, and photographic documentation was performed when feasible.

Data Collection and Stratification: Foetuses were stratified into six Fertilization age groups at two-week intervals: 16–18, 20–22, 24–26, 28–30, 32–34, and 36–38 weeks. Within each group, mean body weight and CRL were calculated. Morphological characteristics were recorded on standardized proformas and entered into a structured database.

Quality Assurance: All anthropometric measurements were taken independently by two trained investigators. Discrepancies greater than 2% prompted re-measurement. All measuring instruments were calibrated weekly. Observers performing lung dissections were blinded to Fertilization age in cases where CRL served as the primary age estimator.

Data Analysis: Descriptive statistics including mean, standard deviation, and proportions were computed for body weight and CRL, lung morphology. As it is a descriptive study, no inferential statistics were applied.

Of the 50 foetuses studied, 29 were females and 21 were males.

 Table 1 presents mean foetal body weights (mean ± SD) across six fertilization‑age groups. At 16–18 weeks (n = 6), the average weight was 275.0 ± 104.9 g. By 20–22 weeks (n = 8), it rose to 625.0 ± 128.3 g, and by 24–26 weeks (n = 8) to 1 150.1 ± 140.5 g. Further growth was steady: 1 550.0 ± 68.6 g at 28–30 weeks (n = 10), 2 010.0 ± 132.1 g at 32–34 weeks (n = 9), and 2 420.0 ± 112.5 g at 36–38 weeks (n = 9). The increasing means with generally smaller variability late in gestation reflect normal foetal development.

This descriptive, cross-sectional autopsy study examined the morphogenesis of lung of 50 aborted foetuses between 16 and 38 weeks of fertilisation age. The sample was evenly distributed by sex (29 females, 21 males) and met strict inclusion criteria that excluded maceration and congenital anomalies.

Our observed steady increases in mean fetal weight from 275.0 ± 104.9 g at 16–18 weeks to 2 420.0 ± 120.0 g at 36–38 weeks and narrowing variability in later gestation reflect the prescriptive growth patterns as found in INTERGROWTH-21^{st 10} and NICHD ¹¹ approaches. The mid-gestation means in this study exceed those reported in a Gujarati autopsy series (158 g at 14–18 weeks and 523 g at 19–26 weeks), ¹² likely due to regional variation.

Crown–rump length (CRL) increased linearly from 150 mm to 335 mm across the study window (Table 2), matching Indian ultrasound centiles that show slightly higher CRL than Western references in early pregnancy. ¹³

All lungs were located within the thoracic cavity and showed no evidence of ectopic positioning. Most lungs were soft, smooth, pinkish-brown, and pyramid-shaped, consistent with stage-specific developmental expectations.

The proportion of pulmonary hypoplasia found in this study decreases progressively as age increased from 100% at 16–18 and 20–22 weeks, to 80% at 24–26 weeks, 50% at 28–30 weeks, 22% at 32–34 weeks, and 0% at 36–38 weeks yielding an overall hypoplasia rate of 70%.  In contrast, neonatal autopsy studies report overall hypoplasia rates near 22% across all gestations ¹⁴, while cohorts with premature rupture of membranes (PROM) show rates of 12.9% ¹⁵. Fetuses with congenital anomalies demonstrate intermediate hypoplasia prevalence (35–43%) ¹⁶, reflecting the impact of sample composition and clinical context on observed rates.

Sajjan et al. reported a similar second-trimester peak of lung hypoplasia (26 %) followed by a sharp decline when lung-weight to body-weight ratios were used. ¹⁷ Neeha et al. also found most pulmonary lesions before 30 weeks in a larger northern-Indian series. ¹⁸ However, our trend agrees with Husain and Hessel’s neonatal autopsy data, which placed nearly all cases of true hypoplasia before 32 weeks. ¹⁴

Externally, lung morphology in our series transitioned from a pyramidal, pinkish-brown, underdeveloped appearance in early gestation (16–22 weeks) through a lobated, light-brown stage with improving lobe definition in mid-gestation (24–30 weeks), to a fully lobated, grayish-pink morphology at term (36–38 weeks). These macroscopic observations correspond closely with classical histogenetic stages: pseudoglandular (branching morphogenesis), canalicular (type I and II pneumocyte differentiation), saccular (sac formation and surfactant synthesis), and alveolar (alveolization). ^{19, 20}

Laudy and Wladimiroff ²¹ describe the same gross transition during the canalicular-to-saccular phase, when vascularity increases, and surfactant production begins. Schittny adds that secondary septa and early alveoli form after 28 weeks, ⁴ consistent with our observation of clearer lobation and colour change in the third trimester.

The developmental timeline in this series aligns with established staging: embryonic (4–7 weeks), pseudoglandular (5–17 weeks), canalicular (16–25 weeks), saccular (24 weeks–term), and alveolar (post–36 weeks). Insults before 16 weeks carry the highest risk of pulmonary hypoplasia, matching our 100% early-week rates, whereas later insults have progressively less impact, paralleling the rapid reduction to zero hypoplasia by term.

These observations reflect the recent MRI-based morphometric studies, which confirm that lung volume and complexity increase progressively in late gestation. ²²

This study documented the morphogenesis of foetal lungs between 16 and 38 weeks of gestation. Pulmonary hypoplasia was common in the early second trimester, decreased markedly by 30 weeks, and was absent beyond 36 weeks, while lung appearance evolved from small, pinkish, pyramid-shaped organs to well-lobated, grey-pink structures approaching adult form. These findings offer useful Indian reference data for assessing foetal growth and lung maturity during autopsy and can assist clinicians in counselling families about viability and development. Larger multicentre studies will further refine these benchmarks.