The office said Manar Ibrahim Karaja, who is five months pregnant, has not received a pregnancy check-up since July 8.
It said Karaja, a mother of two, has also suffered from severe itching and skin lesions resembling symptoms of scabies for more than two months.
According to the office, Karaja’s weight fell from 60kg before her pregnancy to 54kg within 20 days of her detention and has since risen only to 57kg.
The office attributed the weight loss and limited recovery to poor-quality food lacking nutrients needed during pregnancy.
Meanwhile, the office also raised concerns over the health of pregnant detainee Dana Joudeh, who is due to enter her ninth month of pregnancy in early September.
The office called for urgent and regular medical examinations, adequate nutrition and hygiene supplies, and immediate dermatological treatment for Karaja.
It also called for Karaja to receive hospital-based pregnancy monitoring without delay.