how to make infant incubator
Ideally you would force a constant current through the rtd and measure its output voltage, which (after level shifting) would cover the adc input range when operated across your target temperature range. Over such a small temp range, however, this would require an unacceptably huge current.
Even at lower rtd currents you want to watch out for self-heating. So, you can force a current of maybe 500µA through the rtd to avoid self-heating effects and still get a reasonable signal-to-noise ratio. Use an instrumentation amplifier to measure the voltage that develops across the rtd as a result of the constant current excitation. This i-amp will eliminate the common mode voltage and you can inject whatever offset you need to make the i-amp's output 0V at 20°C. Program the i-amp gain so that it outputs 0V at 20°C and it outputs your adc full scale input voltage (5V?) at 40°C.