Save the Children said the bomb, from an air strike, hit the entrance to the hospital in rural Idlib province.
Images show part of the building destroyed. The number of casualties is not yet clear.
The charity says the hospital is the biggest in the area, carrying out more than 300 deliveries a month.
It is not clear who carried out the air strike.
A Save the Children spokeswoman said the hospital treats about 1,340 women and children every month with an average number of 322 births in the same period. The charity supports the hospital through its partner, Syria Relief.
In other developments:
Russia, a key ally of the Syrian government, said on Thursday that three humanitarian corridors from Aleppo were being opened for civilians and unarmed rebels and a fourth for armed rebels.
About 300,000 people are trapped in rebel-held eastern Aleppo, under intense bombardment.
Russia’s announcement was welcomed cautiously by the UN, the US and some aid agencies.
UN envoy Staffan de Mistura said the UN supported such corridors in principle and was asking Russia for more details on how they would work.
“Our suggestion to Russia is to actually leave the corridors being established at their initiative to us,” Mr de Mistura told reporters in Geneva.
“The UN and humanitarian partners know what to do.”
He echoed calls from the UN’s Under Secretary General for Humanitarian Affairs, Stephen O’Brien, for a 48-hour truce to allow aid into the east of the city.
“How can you expect people to want to walk through a corridor, thousands of them, while there is shelling, bombing fighting,” Mr de Mistura asked.
He said the UN was “in principle and in practice in favour of humanitarian corridors under the right circumstances” but said Russia needed to provide more information on how the system would work.
He reiterated that civilians who left should do so only through their own choice.
“The clock is ticking for the Aleppo population,” he warned.
The UN said on Monday that food supplies in Aleppo were expected to run out in mid-August and many medical facilities continued to be attacked.
Russian Defence Minister Sergei Shoigu has said the three corridors for civilians and unarmed fighters would have medical posts and food handouts.
The fourth corridor, in the direction of Castello Road, would be for armed militants, he said.
The Red Cross said on Thursday it welcomed any respite for civilians in Aleppo but that departures must be voluntary and the safety of those who decided to stay must be guaranteed.
The US state department also expressed caution, saying that the exercise appeared to be an attempt to force the evacuation of civilians and the surrender of militant groups in the city.
UK-based monitoring group the Syrian Observatory for Human Rights said on Friday that seven children were among the 28 killed in the coalition air strike on al-Ghandour village near Manbij.
The US confirmed air strikes took place near Manbij on Thursday and said it was investigating claims of civilian casualties.
Manbij is controlled by the so-called Islamic State group but encircled by Kurdish-led forces who are advancing with the support of coalition air strikes.