In a similar situation as your case with the salary differences. I didn't really expect or asked my husband to pay for my prenatal expenses and postpartum expenses unless I really had no means to pay on my own.
My husband is supportive to pay for the expenses that I didn't asked for help as he thinks that it's also his responsibility as a husband and father to our baby to contribute to the expenses. But it can get stressful at times when he is paying more than myself as I can't really afford the bill on my own comfort. So I didn't take those luxury stuffs like massages and confinement nanny as the cost is too much for husband to pay alone and I can't really afford + see the need to
My take is use something like the 1:2 ratio if both your husband and yourself are not that calculative to the cents. If you really feel bad for making him pay, can offer to return by covering for future expenses like baby and household expenses when baby is born. Don't get too stressed during pregnancy and postpartum over who should pay unless it's the case of husband want to have kids but you don't really want.
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