My doubt is when do lung maturity ( surfactant formation) occur

My doubt is when do lung maturity ( surfactant formation) occur
1.By 35 weeks( acc to pediatrics )
2. By 37 weeks ( acc to gyne )

Surfactant production starts around 20 weeks of life and peaks at 35 weeks gestation. Therefore, any neonate less than 35 weeks is prone to develop RDS.

At 35 weeks L/S ratio is 2. L/S ratio > 2 indicates pulmonary maturity. RDS is one of the major causes of death in preterm babies born before 34 weeks. Hence, you can take the cutoff as 35 weeks. Thank you.

Ref: Ghai, 9th Edition, Page 165; DC Dutta, 8th edition, Page 124