I made myself a spreadsheet of what I'd be paying based on each plan my company offered. I figured out my normal usage, then what I'd pay for pregnancy, and developed scenarios for best case, most likely case, and worst case. I then assigned probabilities to each of those happening (not that I'd admit to being such a geek on any other forum!) and figured out a total cost per plan based on the weighted average of the scenarios. For me, it worked out that one plan was the winner only if the best case happened, and another won for average, worst case, and the calculated weighted average. So, it was an easy choice.
If it helps you figure out your costs, a pregnancy usually includes a specialist office visit copayment that covers your entire pregnancy checkups (if you go into a new plan year - are pregnant in both December and January - you probably will have to pay this again), 2-3 lab visits, 1-2 additional copayments for sonogram if they can't do that in house ("imaging" or specialist copay), delivery fee, hospital stay, baby's first checkup from the doctor, and extra fees for anything else you use like drugs, anesthesiologist, circumcision, and hearing test. You can usually find a rough estimate of the costs through your insurance company, and all insurance plans are required to publish a Summary of Benefits and Coverage that includes the cost breakdown for each item and a chart at the end that shows you how they apply the rules for having a baby. Different companies do things differently, so it can be helpful to see how they set it up.
One thing to definitely pay attention to is your MOOP (maximum out of pocket) for each plan. Once you hit that dollar amount, you're not going to pay another penny. That made the plan with a slightly higher premium but much lower MOOP the best deal for us, and is part of why HDHPs are often a great choice when you're staring down huge medical expenses.
It was a lot of math, but doing my best to research costs and actually running numbers really was a helpful exercise that kept us from second-guessing our choices later on, as well as figure out how much we needed to save. FWIW, with my first kid I had a normal pregnancy right until the end, when I had a C-section, needed a plasma infusion, was on blood pressure drugs, and spent an extra few days in the hospital. That one had the standard set of costs I gave you above, but then amounted to about $60k in the hospital for the surgery, anesthesiology, extra drugs, extra monitoring, a plasma infusion, etc. I was on premium insurance, so paid a $500 copay plus like $300 for the stupid surgical assistant they gave me that wasn't covered by insurance (I should've fought that charge!). The second kid, I came down with gestational diabetes and low platelets around 32 weeks. I ended up paying for like 5 extra lab visits, and three extra specialist copays, but since I had a standard, planned C-section my hospital stay was more like $20k before insurance, even though it was the same hospital as my first kid. For the third one, I was being monitored super-closely but they did the labwork and ultrasounds in-house and I didn't pay extra for it. However, we hit that MOOP and hit it hard! I had low amniotic fluid, and so he was born six weeks early. I spent one night in the hospital being monitored before he was born, and he spent two weeks in NICU-lite ("special care nursery"). He had hospital stay and doctor visit charges for that, as well as lab visits and cost for formula and vitamins while he was there. Pre-insurance costs were close to $100k. The good news in that scenario is no matter how expensive it gets, you're pretty much not going to go over your MOOP ("pretty much" = the special care nursery was out of network, even though the hospital was in network. We had to file a few rounds of paperwork with the insurance to get them to cover it in network, and there was no MOOP for out of network so we would've been pretty much bankrupt).